What’s the Warmest Year – and Does it Matter?

Cross-posted from NextGenJournal

Climate change is a worrying phenomenon, but watching it unfold can be fascinating. The beginning of a new year brings completed analysis of what last year’s conditions were like. Perhaps the most eagerly awaited annual statistic is global temperature.

This year was no different – partway through 2010, scientists could tell that it had a good chance of being the warmest year on record. It turned out to be more or less tied for first, as top temperature analysis centres recently announced:

Why the small discrepancy in the order of  1998, 2005, and 2010? The answer is mainly due to the Arctic. Weather stations in the Arctic region are few and far between, as it’s difficult to have a permanent station on ice floes that move around, and are melting away. Scientists, then, have two choices in their analyses: extrapolate Arctic temperature anomalies from the stations they do have, or just leave the missing areas out, assuming that they’re warming at the global average rate. The first choice might lead to results that are off in either direction…but the second choice almost certainly underestimates warming, as it’s clear that climate change is affecting the Arctic much more and much faster than the global average. Currently, NASA is the only centre to do extrapolation in Arctic data. A more detailed explanation is available here.

But how useful is an annual measurement of global temperature? Not very, as it turns out. Short-term climate variability, most prominently El Nino and La Nina, impact annual temperatures significantly. Furthermore, since this oscillation occurs in the winter, the thermal influence of El Nino or La Nina can fall entirely into one calendar year, or be split between two. The result is a graph that’s rather spiky:

A far more useful analysis involves plotting a 12-month running mean. Instead of measuring only from January to December, measurements are also compiled from February to January, March to February, and so on. This results in twelve times more data points, and prevents El Nino and La Nina events from being exaggerated:

This graph is better, but still not that useful. The natural spikiness of the El Nino cycle can, in the short term, get in the way of understanding the underlying trend. Since the El Nino cycle takes between 3 and 7 years to complete, a 60-month (5-year) running mean allows the resulting ups and downs to cancel each other out. Another cycle that impacts short-term temperature is the sunspot cycle, which operates on an 11-year cycle. A 132-month running mean smooths out that influence too. Both 60- and 132- month running means are shown below:

A statistic every month that shows the average global temperature over the last 5 or 11 years may not be as exciting as an annual measurement regarding the previous year. But that’s the reality of climate change. It doesn’t make every month or even every year warmer than the last, and a short-term trend line means virtually nothing. In the climate system, trends are always obscured by noise, and the nature of human psychology means we pay far more attention to noise. Nonetheless, the long-term warming trend since around 1975 is irrefutable when one is presented with the data. A gradual, persistent change might not make the greatest headline, but that doesn’t mean it’s worth ignoring.

Odds and Ends

I must thank Michael Tobis for two pieces of reading that his blog recently pointed me to. First, a fantastic article by Bill McKibben, which everyone should print out and stick to their fridge. Here’s a taste:

Read the comments on one of the representative websites: Global warming is a “fraud” or a “plot.” Scientists are liars out to line their pockets with government grants. Environmentalism is nothing but a money-spinning “scam.” These people aren’t reading the science and thinking, I have some questions about this. They’re convinced of a massive conspiracy.

The odd and troubling thing about this stance is not just that it prevents action. It’s also profoundly unconservative. If there was ever a radical project, monkeying with the climate would surely qualify. Had the Soviet Union built secret factories to pour carbon dioxide into the atmosphere and threatened to raise the sea level and subvert the Grain Belt, the prevailing conservative response would have been: Bomb them. Bomb them back to the Holocene—to the 10,000-year period of climatic stability now unraveling, the period that underwrote the rise of human civilization that conservatism has taken as its duty to protect. Conservatism has always stressed stability and continuity; since Burke, the watchwords have been tradition, authority, heritage. The globally averaged temperature of the planet has been 57 degrees, give or take, for most of human history; we know that works, that it allows the world we have enjoyed. Now, the finest minds, using the finest equipment, tell us that it’s headed toward 61 or 62 or 63 degrees unless we rapidly leave fossil fuel behind, and that, in the words of NASA scientists, this new world won’t be “similar to that on which civilization developed and to which life on earth is adapted.” Conservatives should be leading the desperate fight to preserve the earth we were born on.

Read the rest of the article here. Highly recommended to all.

The other link I wanted to share was a new publication entitled “Science and the Media”, just released by the American Academy of Arts and Sciences (not to be confused with the American Association for the Advancement of Science – why all the acronym duplication?)

With contributions from everyone from Donald Kennedy to Alan Alda, and essays with titles from “The Scientist as Citizen” to “Civic Scientific Literacy: The Role of the Media in the Electronic Era”, I’m virtually certain that I will enjoy this one (sorry, I can’t bring myself to say things like “certain” without caveats any more). The 109-page pdf is available free of charge and can be accessed from this page, which also includes information on ordering hard copies.

In other news, the La Niña conditions in the eastern Pacific (see anomaly map above) have bumped this year’s temperatures down a bit, so January-September 2010 is now tied for the warmest on record, rather than being a clear winner. This analysis is from NCDC, however, and I’m not sure how they deal with sparse data in the Arctic (for background, see this post – a summary of one of the most interesting papers I’ve read this year). Does anyone know if GISS has an up-to-date estimate for 2010 temperatures that we could compare it to? All I can find on their website are lines and lines of raw data, and I’m not really sure how to process it myself.

That’s all for today. Enjoy the week, everyone.