Global warming (or global climate change) continues to be a contentious issue because of the political ramifications of the science. When I talk to those who doubt human-caused (anthropogenic) global warming inevitably they express a strong political opinion about the implications of AGW – that it is being used to justify government take-over of private industry.

There are also those on the left who embrace AGW as a way of reinforcing their ideological economic opinions. None of this makes AGW correct or mistaken. The political implications of AGW are irrelevant to the science.

I might be tempted to say that the controversy over AGW is partly being driven by the fact that the science is very abstract. There is a ton of data that can be used to support just about any opinion you wish to defend, if you are willing to cherry pick. The data is also somewhat abstract and is very complex.

While I do think it’s true that the nature of the data regarding AGW does exacerbate the controversy, I can’t say it is a necessary component, as there are controversies surrounding far simpler rock solid science, such as the efficacy of vaccines.

In any case, AGW does have a particular challenge in that the discussion is very statistical and graph heavy, two things which are easy to manipulate and sow confusion.

99.999%

Several recent claims and studies serve as examples. One recent study seems perfectly legitimate to me, but has resulted in headlines that are a bit misleading until you dig deep enough to figure out what they are really talking about.

The number caught my eye, as scientific conclusions are rarely so solid. The IPCC has placed their confidence in AGW at 95%, which seems like a more realistic number. How, exactly, did they arrive at three decimal places of certainty?

The study is a statistical analysis, not a measurement in the confidence of our current models of the climate. The authors looked at global surface temperatures for the 20th century and evaluated two aspects, overall warming, and the short streaks of cooling (of which there were 11). They then used existing models of known natural drivers of climate and calculated the odds that the observed temperature changes would result from them alone, without human forcing.

Their result was that, in each case, the chance of the observed data resulting from known natural forces was 1 in 100,000. That is where the 99.999% figure comes from.

AGW critics are almost certain to pounce on the fact that these numbers are based on known drivers of climate change. This is not a measure of confidence in our climate models, but rather is based on the assumption that our climate models are correct.

This is more a matter of how to communicate science rather than the science itself. The study is extremely useful, and (assuming it stands up to further review and replication) it does essentially rule out the hypothesis that recent global temperatures are just natural variation. Either humans are forcing global warming, or there is a source of natural forcing currently unknown to science. It is not fair to criticize a study for what it isn’t, rather than evaluate it for what it is.

Michael Mann Strikes Back

Michael Mann is the scientist originally behind the “hockey stick” data – the sharp upturn in global temperatures starting around the beginning of the 20th century. He has become a favorite target of global warming contrarians, who he says have picked him out of the herd like predators on the Serengeti.

The Competitive Enterprise Institute said of Mann:

“Mann could be said to be the Jerry Sandusky of climate science, except that instead of molesting children, he has molested and tortured data in the service of politicized science.”

Mark Stern from the National Review went as far as to call Mann’s work, “fraudulent.” Mann has since sued both for accusing him of fraud, and the trial is ongoing.

At this point in the trial, both sides are filing briefs on the scientific legitimacy of Mann’s work. It is always interesting when public debates are subjected to the rules of evidence in a courtroom. As we saw with the Kitzmiller v. Dover Intelligent Design case, real science has a distinct advantage when there are rules of evidence.

As reported by the Union of Concerned Scientists, the CEI and NR briefs on the matter have not been impressive:

What’s missing, of course, from all their briefs, are legitimate scientific citations rejecting or refuting Dr. Mann’s work. That’s because those don’t exist.

Since the original publication of his work, it has been not only validated but replicated extensively. It is no longer a viable scientific position to argue that global warming is not happening.

Polar Ice

For the second year in a row, arctic sea ice has increased. That is the kind of statistic I hear all the time (dealing with any politicized issue) – it superficially implies a certain conclusion, but it does not provide enough data to really interpret it.

Phil Plait recently covered this issue nicely, so I won’t rehash all the details. The short version is that arctic ice has been in a consistent downtrend for decades. The trend is absolutely clear – arctic sea ice is going away. Arctic ice hit a record low in 2012, and since then has regressed to the mean, so that the last two years have increased. The overall downward trend, however, is unchanged.

This is a way of cherry picking data – choose a starting point for comparison that is anomalously low, then point to the subsequent increase.

The situation in the antarctic is a bit more complex. Antarctic sea ice has increased recently. It is not clear why – perhaps a combination of increased precipitation and other factors. It is not because of decreased ocean temperatures, which continue to rise.

However, pointing to antarctic sea ice increasing as evidence against AGW is more cherry picking. Antarctic land ice is decreasing. This is also the ice we care about, as melting land ice raises ocean levels, while sea ice has little effect because it is already displacing water.

Further, if we look at global sea ice, it has been decreasing by about 1.4% per decade. The overall trend is decreasing, even though there are local temporary increases.

Conclusion

The science is fairly certain at this point – overall global temperatures, if you look at all the data, have been increasing over the last century. The trend is undeniable. Further, natural known factors cannot explain this trend. The most likely cause is human-caused greenhouse gas emissions.

However, this set of data is complex. There are many short term and local trends within the data, creating endless opportunities for cherry picking.

I can understand that people have different political perspectives on how to deal with AGW. I am not taking political sides here. I just think that the politics need to be separated from the science.

First, we need to get the science right. Then we need to use that science to inform the political discussion.

We need to have the maturity and perspective to respect the science, even when it is inconvenient for our ideological position. It’s OK to say, “AGW is real, but I don’t think carbon taxes are the solution,” or whatever is your position.

People desire simplicity and purity, however, and formulating nuanced positions incorporating competing facts and principles is hard work. Those who have political problems with the implications of AGW want all the science to go in their direction as well.

However, the universe does not seem to care about our political values.

I also think you undercut your political position when you anchor it to bad science or science denial. This sucks the legitimacy out of your entire position. Get the science right, then advocate for solutions in line with your values.