Before I get into how we know the creation hypothesis is incorrect, I would like to address a more philosophical point. We live in a culture that encourages us to have strong opinions, be it about whether politician X should be president or whether Jersey Shore can be considered “culture.” Is this a good thing? Maybe, maybe not. It is good to disagree; it keeps life interesting and ensures that we are exposed to many different viewpoints. Currently in our culture, there are several disciplines of science that are subjected to this type of handling. I would argue that this does a great disservice to our society.

Unlike opinions on politicians or TV shows, scientific arguments are fundamentally data driven. This is not to say that there are not philosophical arguments; there are and they are vitally important, such as the paradigm shift from thinking that natural selection acts on the individual to thinking that it acts on genes. But ideas such as these represent new ways of interpreting existing data. For opinions to be formed, you must first examine the data and then decide whether you accept it or reject it. This is difficult enough for scientists, never mind a layperson. The explanations that make their way to pop science books, even the best of them, are too broad and too lacking in nuance. It takes a lifetime of dedicated study to truly understand even one sub-discipline. And yet we as a society are not humble when we debate scientific ideas. Everyone has an opinion, often formed on the basis of what the pundtocracy says. This is a problem for both the left and the right, whether it be about vaccines, climate change, or evolution. In science, opinions require evidence. We ignore that in our public discussions; rhetoric is far more persuasive. I cannot speak for anyone else, but I approach any new idea in science in two ways. The first is to remind myself that I am not an expert and the person who wrote the paper generally is. The second, which is how science is taught in college, is to assume that there are problems with the paper and to look for them. No ideas are perfect; reality is complicated. Even papers that are published in premiere journals have flaws. With that being said, these papers are (usually) mostly correct. It is from this approach to data that opinions about scientific ideas should be drawn.

With that introduction, I would like to directly address the comment. In particular the question “how would we know” because, while the answers are well established, they are not well known in our society and are often not taught to our children in school. Rather than deal with my own field of evolution, I would like to address the other aspect of creationism: the idea that the Earth is the product of special creation and is relatively young (say, less than 10,000 years old). This is an opinion that is common in our society; depending on what poll you look at, up to 40% of our country agrees with that sentiment. But it is an opinion not founded on data. Below I will explore three of the entirely independent lines of evidence available to all of us.

I will begin with the cosmological evidence. When we look through our telescopes, we are looking back in time. When you gaze upward at the Sun you are seeing light that is a little more than 8 minutes old. This is because of one of the laws of nature: the speed of light is finite. We know it to be roughly 186,000 miles per second. The distance light travels in one year is termed a light year. Combine this with the knowledge that space is expanding and we can form a testable hypothesis: if the universe was specially created in the past 10,000 years, we should not be able to see objects that are more than 10,000 light years away. This is, of course, not what we see when we look through telescopes. The nearest galaxy to our own, Andromeda, is 2.5 million light years away. We can infer from our observational data that the universe is roughly 13.75 billion years old. I would like to stress that this is a well established idea among scientists and there has been no evidence presented that suggests it is false.

A separate line of evidence is based on the idea of radioactive decay and the use of radiometric dating. Certain elements are unstable and thus experience what is known as radioactive decay until an atom reaches a stable state. For example, carbon-14 decays into nitrogen-14. Another example is the decay of uranium-238 through 13 other states before becoming lead-206. The reason radioactive decay is significant is that each unstable isotope has what is known as a half-life: the amount of time for half of the element in a given sample of matter to decay. Each half-life is measurable and is distinct for each element. In the case of uranium-238, its half-life is 4.5 billion years, whereas lead-210, an intermediary between uranium-238 and lead-206, has a half-life of 160 microseconds. Because there is such a wide range of radioactive clocks available, we can not only date objects found, but we can also use several independent measures to date the objects. Based on meteorites found on Earth, meteorites found on Earth that originated on Mars, and rocks found on the Moon, scientists have determined that the Earth is 4.54 billion years old. However, there is another way of corroborating this. Our Sun is what is known as a G-series star. We can observe other G-series stars with our telescopes and these stars are at varying stages of their life spans. (Over time, the size and luminosity of stars change). Because of this, we know that the Sun is 4.57 billion years into its life cycle. Soon we will be able to observe planets forming around other stars and provide a similar corroborating check on the age of the Earth.

The final line of evidence I will highlight is biological, meaning that I am far more comfortable talking about this. All life that we have discovered on Earth encodes its genetic information in DNA (with the exception of most viruses, which use RNA, but for our purposes there is no real difference). Let’s start with a simple example before we delve too far into this. Let’s assume you have one brother and one cousin. All three of you look fairly alike, but you are closer to your brother than you are to your cousin. Or put another way, you all have nearly identical DNA, but your brother’s DNA is closer to yours than your cousin’s is. Now let’s change the time scale to hundreds of millions of years. We know that all species share a common ancestry from at least 3.8 billion years ago. Obviously over time we have diverged; you do not look or behave like your pet dog, never mind the trillions of bacteria in and on your body. This is because DNA mutates over time. One particular type of mutation is relevant here: silent, also known as neutral, mutations. DNA is made up of pairings of four nucleic acids. These pairings form groups of three known as codons, which encode for particular amino acids, which in turn form proteins, which perform functions in your cells. There are twenty amino acids. If you do the math, you realize that several different codons code for the same amino acid. A neutral mutation is one in which the codon changes, but the amino acid stays the same, meaning that there will be no selection for or against the mutation because there is no change in the effect of the codon. This means that neutral mutations will accumulate in genomes at a particular rate. This concept is known as the molecular clock and is used to determine how long ago two (or more) species diverged. This is compared to fossil evidence, which is radiometrically dated, to confirm the accuracy of the molecular clock. I will leave it at one example. Our closest living relatives are chimps. We know from both molecular and radiometric clocks that we shared a last common ancestor with chimps 5 to 6 million years ago. That is a bit more than 10,000 years.

I know this has been a long post, but thank you if you are still with me. I would like to end with explaining why all of this matters to you. There are two sets of reasons. The first is the rather mundane and practical. Much of modern medicine is based on concepts that are true because evolution occurred and continues to occur. And all electronics and nuclear physics are based on the same concepts that tell us how old the universe is. In other words, our society is completely dependent on these ideas, yet many of us reject them. It matters if voters do or do not understand why overuse of antibiotics in livestock is a dangerous practice. It matters if voters do or do not understand that the next deadly virus will probably arise in poverty-stricken bushmeat hunters in Africa. And while it does not really matter if you understand how your computer works or not, society would not be able to function unless a few people did.

For the second reason, I must defer to Carl Sagan and quote him at length. In an essay published in 1995, Sagan wrote, “The truth may be puzzling. It may take some work to grapple with. It may be counterintuitive. It may contradict deeply held prejudices. It may not be consonant with what we desperately want to be true. But our preferences do not determine what’s true.” However, this is not meant to be a negative message. In his 1994 book Pale Blue Dot Sagan wrote, “…if our objective is deep knowledge rather than shallow reassurance, the gains from this new perspective [science] far outweigh the losses. Once we overcome our fear of being tiny, we find ourselves on the threshold of a vast and awesome Universe that utterly dwarfs – in time, in space, and in potential – the tidy anthropocentric [universe] of our ancestors.” Truth matters and, as we have found in every discipline of science, truth is far more inspiring than anything our ancestors imagined.

But why does our sense of awe and wonder matter? Pale Blue Dot gives an answer: “The visions we offer our children shape the future. If matters what those visions are. Often they become self-fulfilling prophecies.” To ensure the future vitality of our society we must provide our children with something to dream about. One tiny subdiscipline of one branch of science can provide any child with more than a lifetime’s worth of dreams. In his comment, Cliff wrote that he would not dismiss someone who did believe creationism. I think dismiss is the wrong word; pity perhaps. But any given individual’s beliefs matter less than society’s as a whole and a society that does not embrace the knowledge discovered by its scientists is consigning itself to decay and decline. The golden ages in history centered on science and invention. So let us inspire our children with the truth. It is the surest guide to the future success and prosperity of our country.

In Monday Perry opened his campaign with this statement: “We’re calling today on the president of the United States to put a moratorium on regulations across this country, because his regulations, his EPA regulations are killing jobs all across America.” To begin with, I think it is worth noting that this is a fairly nonsensical proposal; it’s just that it makes for a good sound bite. The key to understanding what Perry is trying to get at is his reference to the EPA, this week’s Republican punching bag. I do not dispute that EPA regulations mean that there are less jobs out there. I just prefer to refer to EPA regulations as those government policies that are keeping your children from having bone cancer and malformed brains. I will leave it up to you to decide which is your priority.

Also on Monday came the bit about the Fed. “If this guy [Fed Chairman Bernanke] prints more money between now and the election, I dunno what y’all would do to him in Iowa but we would treat him pretty ugly down in Texas. Printing more money to play politics…is almost treasonous in my opinion.” Let’s set aside the standard violent rhetoric, which at this point is a litmus test to prove you are in fact a Republican. And also let’s set aside the fact that Governor Perry meant sedition, not treason, except to note that he should be familiar with sedition as he did advocate secession. That leaves us with him not wanting the Fed to print money between now in the election. Also known as helping the economy recover. Also known as doing what the Fed is required to do by federal law.

Wednesday brought us an interesting statement on climate change. “I think there are a substantial number of scientists who have manipulated data so that they will have dollars rolling into their projects” was the highlight. I think this can best be explained as follows. As has been well documented, those scientists who deny anthropogenic climate change have selectively chosen data so that the oil and coal companies will continue to fund their research. In Governor Perry’s mind, this means that obviously the scientists who think the opposite must behave the same way. There are a few problems with this logic, but I think the most obvious one is that the money he is talking about comes from grants that are generally funding by the federal government. So is Perry accusing Congress of buying off thousands of scientists? Congress is responsible for the claims about anthropogenic climate change?

Thursday was my personal favorite. Approached by a young boy in New Hampshire asking about the age of the Earth and evolution, Governor Perry gave us this gem. “How old do I think the Earth is? I don’t have any idea. I think it’s pretty old. It goes back a long long ways. I’m not sure anybody actually knows completely and absolutely how long ago the Earth is. I hear your mom was asking about evolution. It’s a theory that’s out there and it’s got some gaps in it. In Texas, we teach both creationism and evolution in our programs.” Phew. The first part can obviously be read as his way of trying not to sound crazy while not angering the religious right: “pretty old” is pretty ambiguous. (If anyone is wondering, the answer is 4.54 billion, which is 4,539,994,000 more than many of Perry’s supporters think). As for evolution having “some gaps in it,” well, so it does. If his point is that something else (ie, creationism) might better explain life on Earth then we can just label him as ignorant and/or pandering and move on. His last sentence takes the cake though. Let’s translate. “In Texas, we teach both creationism and evolution in our programs in direct violation of two United States Supreme Court decisions.” After that, Perry did say this: “I figure you’re smart enough to figure out which one is right.” So I think we can illustrate Governor Perry’s plank on education as this: let’s teach our seven-year-olds that there are two equal, competing hypotheses about the shape of the Earth and let them decide which is correct: scientists overwhelmingly say it is round, but there are some people who believe it is flat.

I was born between STS-31 and STS-41, the 35^th and 36^th shuttle missions, both flights of the shuttle Discovery. STS-31 was the mission to deploy the Hubble Telescope. I have never known anything but the shuttle program. Quite frankly, I have taken it for granted; I cannot imagine it being over. But after tomorrow the United States will no longer have the ability to put astronauts into orbit; we will be reliant on Russian Soyuz rockets for the foreseeable future. Not only is there no plan to replace the shuttle, but now Congress is preparing to cancel the Webb Telescope, which was to be the successor to the Hubble, taking us back even closer to the Big Bang than Hubble is capable of.

The shuttle is the most complicated machine ever built, consisting of over a million moving parts. The time and work involved in preparing a shuttle for launch is unimaginable. The shuttles have given us the Hubble and the International Space Station. And they have given us more technological and scientific breakthroughs than most of us will ever know.

In the early 1990s, Congress halted plans to build a supercollider in Texas, opening the door for Europe’s CERN to build the largest supercollider in the world. Cutting-edge particle physics is now done in Europe; European labs will be the ones to unlock the next great secrets of the fundamental building blocks of nature. Now the future of both American astronomy and cosmology, in the form of the Webb telescope, and spaceflight are in question. At a time when more and more countries are developing the means to reach space, we have focused our attention elsewhere.

It could be said that we have greater priorities to focus on; a space program is simply too expensive for our time. But we know that the Apollo program gave back far more to the economy than the government spent. We also know that many of the greatest discoveries in science were mere accidents, the results of exploration for exploration’s sake.

However, for my generation at least, I think there is a more important argument to be made. The shuttles represented one of America’s greatest achievements in its history. They were a symbol of national pride and an inspiration to us all. Now where will that inspiration come from? How inspired will we feel when it is Chinese astronauts, not American, who become the first humans to land on Mars? Will we stand idly by while the other nations of the world surpass us in technical capability?

NASA’s future remains uncertain, as does the future of the American scientific community as a whole. Our schools are failing to teach students basic science. Half of our graduate students in science and engineering are foreigners. And we have no vision for the future.

When President Kennedy gave his famous speech in 1961 declaring that, by the end of the decade, the United States would put a man on the Moon, we did not have the rockets to get there. We did not have a design for a lunar lander, never mind had we built one. We had not even yet put a man into space. My hope is that another President Kennedy will step forward and call on us to surpass what we think is possible.

But, in the meantime, you can watch Friday’s launch on NASA’s website here. And, if you wish, NASA has released an amazing documentary about the shuttle program, which can be watched here. I urge you to watch both; they mark the end of one of the finest periods in American history. They also mark the end of one of the greatest scientific achievements in human history.

The main idea driving the interest in gold is the fear that the US dollar will eventually collapse. Baring a failure to raise the debt ceiling before August 2^nd, the probability of this happening is effectively zero (discussed at end of post). Besides, a collapse of the dollar would lead to a worldwide depression far worse than the Great Depression; I doubt having a form of currency based on a traditionally precious metal will be our greatest concern.

Investing in gold is actually a fairly risky action for a number of reasons. The first is that the price of gold, assuming the current trend of holding it rather than spending it continues, is effectively a function of how quickly it can be mined in South Africa. If the relevant companies mine a lot, the price will go down. If they mine a little, the price will go up. It has little to do with the actual intrinsic value of the metal, which is, if we are honest with ourselves, not that great.

But let us assume that gold does become a normal form of currency. What happens then? Well, as the amount of gold being used for currency increases, one would expect its value to fall. This would mean that any gold you held would be becoming increasingly less valuable. That doesn’t exactly seem like a great investment.

The market, as opposed to the advertisers on TV, is still making it very clear that US Treasury Bonds are the safest investment available. There are no indications from the bond market that investors think the US is facing a debt crisis or that the dollar is at risk. In fact, rates are currently falling, presumably due to both political parties contemplating austerity measures, indicating the investors are worried about more economic stagnation (due to austerity measures).

About a week ago, the New York Times ran a story about the campaign to pass this law. The article focused mostly on one of the main advocates for the law, though it did briefly quote one of the main opponents, a former Republican state senator. For once we weren’t subjected to the same tired old excuses, that government has no place in the healthcare market, meant to protect the healthcare industry.

The argument, also used during the fight over national healthcare reform, was that the new healthcare law, specifically the new taxes that would be necessary to enact it, would drive businesses from Vermont. This is an argument that of course makes little sense; Vermont will be replacing its current healthcare system with a cheaper one. Businesses that currently provide healthcare to their employees will almost certainly see a fall in their expenditures on healthcare. Yes, businesses that do not provide healthcare to their employees will be negatively impacted, but are these the type of businesses one wants in their state?

With that being said, the practical arguments are all rather beside the point. The question of healthcare policy is a question of ethics: our citizens’ lives and livelihoods are at stake. It is a moral failure to ignore that fact, yet we so often do so.

In response to the former state senator’s claim that the healthcare law would drive businesses from Vermont, I have one very simple question, one that has never been answered by opponents of increasing access to healthcare: how many jobs is one human life worth?

We know without a doubt that tens of thousands of Americans die every year for lack of access to adequate healthcare. We also know that untold numbers more are far sicker than they need to be due to a healthcare system designed with little interest in actually improving health. So when an argument is presented in opposition to increasing access to healthcare, it must be weighed against the lives lost and ruined under the current system. In this case, the opponents of reform have placed the potential loss of jobs on the scale. So a rephrasing of my question: what number of dead and sickly citizens of Vermont balances the scale against the jobs that might be lost due to this law?

This debate should remind us that the opponents of healthcare reform, both on the state and national levels, in their crusade to protect the liberty of corporations, have engaged in an endless assault on individual liberty. The two do not have to be mutually exclusive; unfortunately, the defenders of corporations have forced our nation to decide between the two. I for one am glad to see that at least one state has decided that the two are compatible and has enacted a law that both respects human dignity and improves the financial condition of businesses.

The talk was given by Harvard Law School Professor Lawrence Lessig, who teaches constitutional law and institutional ethics. The talk focuses on how we as citizens can and must fix our broken political system. Professor Lessig includes a fascinating history lesson and gives quite a compelling argument. But perhaps what is most striking about his talk is that Americans of all political persuasions, I think, will agree with him and can unite around his plan for reclaiming our representative democracy.

On January 28^th a report was published in the journal Science entitled “Defeating Creationism in the Courtroom, But Not in the Classroom.” The researchers sought to survey what our students are currently being taught in biology classrooms. The results were not promising.

They found that only 28% of American biology teachers instruct their students in evolution as recommended by the National Research Council, which works in conjunction with the National Academy of Sciences. In other words, only 28% of our teachers are teaching students basic biology.

What I personally found shocking was that a full 13% of our biology teachers outright teach creationism in their classrooms, something that has been declared unconstitutional by the Supreme Court on at least two occasions. What was not surprising was that the remaining 60% attempt to avoid the controversy, either by failing to teach evolution or by avoiding the more “controversial” topics in evolution (such as the divergence of species).

I say this is not surprising because a rather large fraction of our country does not “believe” in evolution. Not only are the parents who belong to this group vocal in their opposition to allowing their children access to a century and a half’s worth of scientific research, but they have also proven themselves to be quite adept at taking over school boards. Every few months we see a story of yet another school board that wants to “teach the controversy.” Fortunately these districts’ lawyers have also proven themselves to be adept at reading Supreme Court decisions.

I think that there are two major problems here. The first is that we are denying the majority of our nation’s children access to an adequate science education. Evolution has been the accepted explanation for the phenomenon of life since at least the 1870s. By what right do we deny children access to these ideas? And in what universe does it make sense to ensure that our children have inadequate science educations? Does anyone really think the Chinese or Japanese have to deal with this issue?

The second major problem is that evolutionary biology has very important public policy applications that Congress has so far ignored, much to the detriment of your chances of dying of old age. Chronic diseases are currently the largest medical problem in the United States (and these have evolutionary explanations), but the two most terrifying phenomena are drug-resistant bacteria and the transfer of pathogens, especially viruses, from animals to humans. Both are examples of evolution in action. Both are extremely fatal. In the past decade we have watched, for the first time since World War II, Americans die of incurable bacterial infections. These bacteria have evolved drug resistance. As for the second category, the classic example is HIV.

Our nation can ill afford to continue to ignore an entire discipline of science, especially the one that forms the basis of medicine. Yet we have been fighting about evolution since Louis Agassiz and Asa Gray debated Darwin’s ideas in Boston 150 years ago. It is utterly incomprehensible.

The theory of evolution is one of the most powerful and most beautiful concepts ever discovered by science. By understanding it, one can actually begin to comprehend the natural world. It tells us the history of life and how we came to be the way we are. We owe Darwin, and the other great biologists who have added to his ideas, a great deal. President Lincoln was born on the same day of the same year as Darwin and that coincidence has not gone unnoticed. These two men have sometimes been referred to as the two great emancipators. And lest that seem too pretentious a comparison let us remember that science, as the great biologist E. O. Wilson has written, “aims to save the spirit…by liberation of the human mind.” We do not celebrate just Darwin the individual today; rather, we celebrate the fact that we can say with some certainty that we understand the world around us.

Much to my surprise, I found what I was looking for on Matt Taibbi’s blog today. The post can be read here. For those of you unfamiliar with Taibbi, he writes Rolling Stone’s political affairs column and is one of the more bombastic liberal commentators out there, though he is far from being a partisan Democrat; you’re as likely to read him attacking the Democrats as the Republicans and he is perhaps most well known for his attacks on the excesses of Wall Street.

Now, Taibbi, to the best of my knowledge, has never engaged in violent rhetoric, unless we’re counting comparing Goldman Sachs to a vampire squid as inciting violence. Rather, he is guilty of what so many commentators have done in recent years: excessive rhetoric demonizing their opponents. That being said, Taibbi is rather tame by Fox News standards; there’s a difference between claiming members of both parties are unfit to govern and claiming that the Democrats are destroying our country.

But Taibbi is, to the best of my knowledge, the only member of the media to step forward and say, “We should be held to a higher standard.” Whether he reverts back to bombastic rhetoric remains to be seen. But the fact that he was able to say that he was guilty of behaving irresponsibility. This is a step above what we’ve come to expect of most of the members of the media and our political leaders, who all seem to be in a rush to blame anyone but themselves. In fact, the only politician I can really remember taking responsibility for something going wrong is the President.

Taibbi’s post is, I think, what we want from the media and politicians. Or at least, what the rational centers in our brains want. He acted like an adult, taking responsibility for his past mistakes, regardless of the fact that they had absolutely no connection to what happened in Tucson. Somehow I doubt many other opinion makers will do the same. If anyone knows of a similar statement, please post it in the comments. I think we all know that most of the people who have used irresponsible rhetoric will continue acting like children, shifting the blame to their critics while never acknowledging their own mistakes.

Taibbi’s post touches on why we won’t see many like it. The reason we hear this rhetoric, from the media and from politicians, is that there is a market for it. Pundits and politicians are selling a product, and partisanship is in heavy demand these days. In the end, it is us, the consumers and voters, who are responsible for the violent rhetoric we hear. If we were not energized by it, increasing media profits and voting turnout, the pundits and politicians would not use it. I personally would like to live in a society where it is unacceptable for politicians to use the rhetoric of violence, where doing so would effectively end their political careers, but that’s not going to happen. In the wake of the shooting, CBS conducted a poll asking whether violent action against the government was ever justified. In April 2010, the percentage of respondents who said yes was 16%. After the events in Tucson, the number stayed level at 16%. This should be troubling to anyone who values living in a republic.

I begin with the discovery of hundreds of exoplanet candidates in our galaxy. This does not mean that astronomers have found hundreds of exoplanets (though, with 100 billion stars in the Milky Way, it’s safe to assume that there are at least billions of planets). Rather, using indirect measurements, astronomers have found what look to be planets. As better telescopes (well, spectrographs) come online, astronomers will be able to confirm whether these are in fact planets.

There was one other very interesting find when it comes to exoplanets. In September one team of researchers was able to identify the first exoplanet known to hold liquid water. However, this discovery was contested when a second team could not find the planet. Whether the planet does exist and does contain water will remain in question; however, there is no question that somewhere out there exist other planets that do contain liquid water. Astronomers are currently looking for planets that have “biomarkers,” or the correct elements and compounds that would allow for life. Carbon. Oxygen. Water. Methane. Carbon dioxide. As well as uranium, potassium, and thorium to allow for tectonic activity. It may very well be that life exists within our solar system (Europa, Titan, Io, and Enceladus are all candidates).

The larger point here is that, at this point, it is very hard to assume that we are alone. The probability that there is other life at least in our galaxy, never mind our universe, is at this point very high. There is a natural tendency to think that this life would resemble something from Earth, presumably much like our bacteria. But it is worth remembering that we really cannot conceive of something that is truly alien; just think about Hollywood’s best attempts and you will understand my point.

The second breakthrough came from Craig Venter’s lab, which created the first self-replicating synthetic genome. They did not create new life. Rather, they created a synthetic copy of the genome of one bacterial species. They then put that genome into a cell that did not contain DNA and belonged to a different species. The cell then began metabolic processes and replicating. My opinion is that this was a great technological achievement, considering how difficult it was to create that synthetic genome. However, the importance is, in my opinion, in the future potential of synthetic biology.

One line of research will be to expand our knowledge of biology by taking existing genomes and altering them by removing genes to see what happens to the cells. Biologists will potentially be able to determine the effect of these genes, as well as the effects of having a smaller genome.

However, there is a more significant implication. Once the aforementioned work is completed, something that will take decades at least, biologists will be in a position to begin attempting to design synthetic life. In effect, humans should one day be able to design living organisms on a computer and then bring these organisms to life. There is great potential here, both for energy generation and for medicine. However, I am getting far, far ahead of the field. This is a field of research that will play out over the rest of the century.
The third great accomplishment was the sequencing of two ancient hominid genomes: in April and again in December work was published on what are now being called Denisovans from Siberia and in May the compete sequence of a Neandertal from Europe was published. The fact that biologists were able to sequence these ancient genomes is amazing in its own right. However, for the general public the significant part was that both genomes reveal evidence that both species interbred with our own.

Some of you may remember the philosophical questions that were raised in the wake of the evidence that Neandertals and humans interbred; the same questions apply to the interbreeding with the Denisovans. In both cases, the genes from the other species are present in only some population groups, meaning not all humans have these genes. Some people have raised concerns about how we define “human.” However, I think such concerns are pointless.

There is a tendency to envision evolution as a straight path, from ancestral species to current species. In reality, the process is much messier. It makes perfect sense that these species would interbreed. Our definition of species is temporal; species change constantly. The discoveries of the interbreeding shed light on how poorly we are prepared to deal with thinking about how the natural world really works; our incessant need to categorize seems to break down. The question ‘are you more or less human if you have these genes?’ is pointless, yet we all want to ask it.

There is still much work to be done on fleshing out the human family tree; archaeologists have seven million years to work with since our divergence from chimpanzees. Much happened during that time and our understanding of what happened when and why is extremely incomplete.

There are, I think, deep philosophical questions raised by each of these discoveries, but I do not wish to get into them here. The one point I will make is that these discoveries have highlighted something all scientists were already aware of: our understanding of reality is still far from complete and science has much work to do. The next decade will probably be a great period of medical progress, but one cannot help but wonder what new fossils will be discovered, how many habitable exoplanets will be found, and what new fields of science will be founded.

Before I can explain forcings, there is an important concept that we need to remember from high school physics: every system is in an energy equilibrium (the second law of thermodynamics). This applies to the Earth, meaning that the Earth must radiate as much energy as it absorbs. Translated into what actually happens, the Earth must emit as much energy as it absorbs from the sun, meaning that if the amount it absorbs rises, the Earth’s temperature must rise to compensate.

A forcing is anything that perturbs that balance, by either raising or lowering the amount of energy the Earth absorbs from the sun. Positive forcings raise that amount, mostly by trapping sunlight that has already entered the Earth’s atmosphere and has been reflected off the Earth’s surface, preventing it from escaping into space. Negative forcings raise the albedo of the Earth, meaning that they increase the amount of sunlight the Earth reflects.

You’ll notice that human activities have caused positive (red) and negative (blue) forcings, meaning that humans have put pressure in both directions. However, you’ll notice the bar at the bottom showing “total net human activities,” which is clearly positive.

There has been a focus on carbon dioxide for two reasons. First, it is by far the largest forcing. Second, it is much longer lived in the atmosphere than other greenhouse gases. While methane (CH₄) is a much stronger greenhouse gas, it only remains in the atmosphere for about ten years. In contrast, carbon dioxide lasts for millennia.

It is important to note the size of the error bar on “cloud albedo effect.” The two aerosol categories are the result of burning fossil fuels, just like greenhouse gases. Many of you will remember the acid rain problem from the late 1980s, which was effectively reduced by the first Bush Administration by implementing a cap and trade policy. These are the same compounds. The reason for the large error bar is that the US Government has so far been unwilling to fund an accurate measure of the aerosol content of the atmosphere.

Aerosols only last about two years in the atmosphere. This means that, were humans to stop burning fossil fuels, the aerosols would all immediately leave the atmosphere, while the carbon dioxide would remain, increasing the pace of warming. If all emissions were to stop today, it’s estimated that temperatures would continue to rise for 20 to 30 more years. They would then stay elevated for over 10,000 years.

The chart measures the net effect of all of these forcings between 1750 and 2005. You’ll note towards the bottom that the researchers included “solar irradiance,” which is the amount of warming that can be attributed to the sun. Many climate change deniers like to assert that the warming is being driven by solar activity, which seems ridiculous when you realize what a small forcing it is. There is, however, a small chance they are correct. Ironically, if they are correct, it means that climate change will be unimaginably more severe than current projections.

Once again we have to return to the error bar on “cloud albedo effect.” If the albedo effect is very large (so at the far left of the error bar), then it would be effectively cutting the warming due to carbon dioxide by a third from current estimates. This would mean that much more of the observed warming has been due to solar activity, as the deniers maintain. However, remember the behavior of aerosols: they last only two years in the atmosphere. Eventually, humanity will have to stop burning fossil fuels; the forcings from greenhouse gases will continue to increase as we burn more. When that happens, the aerosols will be gone, and the net forcing due to human activity will be substantially higher than the current projections.

The chances of this are rather slim; you’ll note that the median of that error bar is still very low. My point in explaining this was simply to show the absurd nature of the arguments of the deniers. There is simply no evidence that the sun has been driving more than a tiny fraction of the warming. And, if it were in fact responsible, then the climate crisis is even larger than the worst scare mongering has predicted.