Jan 22 2010

NASA – Last Decade Warmest on Record

I have never had a strong opinion on global climate change. The data is too esoteric and complex for a non-specialist, in my opinion, to have a firm grasp on it. So climate change is one area where I am content to defer to the consensus of expert opinion. I understand the basic arguments, and find them plausible and even compelling. I have listened to the dissidents, and do not find their arguments compelling. Maybe they have a point about the limitations of our ability to project climate into the future and understand all the consequences and remedies. Otherwise I find their argument severely wanting.

To be fair, “dissidents” comprise a fairly broad range of opinion in my experience, from mild skepticism to dedicated ideological denial. So they defy a single label or attempt to characterize their position, and any such attempt inevitably leads to angry responses from those who feel they have been treated unfairly. And further, there is ideology and extremism on the other side as well.

For me – probably like most people, I just want to understand the facts. I don’t really have any ideological stake in this debate. If there is anthropogenic global warming (which there seems to be) I think we should take reasonable steps to mitigate it. If there isn’t, then I don’t want us to waste our resources chasing our tail.

The most basic factual question is whether or not average global temperature is increasing. It seems like this should be a fairly straightforward question, but on closer inspection it is quite complex. But despite this, it seems like the kind of data that should easily lead to a consensus of scientific opinion. From my reading it has, but this scientific consensus has not translated into a public consensus. At times I hear dissidents say that they accept the climate is warming, they are just not convinced it is anthropogenic. Yet it also seems dissidents will seize upon any opportunity to cast doubt on whether or not warming is even occurring.

Certainly the public political dissidents from AGW deny the warming. George Will, who writes occasionally on this topic, has been repeating the claim that temperatures have leveled off, and may even cool. He wrote in his column:

By asserting that the absence of significant warming since 1998 is a mere “plateau,” not warming’s apogee, the Times assures readers who are alarmed about climate change that the paper knows the future and that warming will continue: Do not despair, bad news will resume.

Pat Buchanan has called global warming a “hoax and a scam” and doubts that warming is even happening.

And of course when the climategate e-mails broke they were followed by accusations that the basic premise of AGW – rising global temperatures – was scientific fraud.

So is the Earth warming or not? NASA is an agency that gathers information relevant to this question. They recently released their analysis of the last decade and concluded that average global temperatures from 2000-2009 in fact were the warmest on record – since we began directly measuring temperatures in 1880. 2009 was tied for the second warmest year on record, despite an unusually frigid December. This is based on the pooled data from many sources:

GISS uses publicly available data from three sources to conduct its temperature analysis. The sources are weather data from more than a thousand meteorological stations around the world, satellite observations of sea surface temperatures, and Antarctic research station measurements.

Other research groups also track global temperature trends but use different analysis techniques. The Met Office Hadley Centre in the United Kingdom uses similar input measurements as GISS, for example, but it omits large areas of the Arctic and Antarctic where monitoring stations are sparse.

Although the two methods produce slightly differing results in the annual rankings, the decadal trends in the two records are essentially identical.

That sounds pretty solid. But there is so much complexity in gathering and assessing this data, that it is unlikely to convince any global warming skeptics. Already they are posting their doubts about NASA’s data.

Here is my layman’s understanding of why the data is so complex. First, we are trying to compare temperature measurements from across decades. This assumes that the method of measurement is consistent – same instruments and calibration under the same conditions. If a building was added in 1940 that throws a shadow on a measuring station, then that changes the measurements. Or if different shielding methods are used to prevent direct warming by sunlight. Often temperature data needs to be adjusted to account for these changes – adjustments introduce the opportunity for more judgments and mistakes, and therefore more doubt.

Perhaps the largest source of confusion about temperature data is that climate scientists are trying to pick out a trend in average temperatures, which is tiny compared to the variations in temperature. Of course, temperatures vary greatly throughout each day, they will change with cloud cover, and they will vary by season. There are also numerous short term and local trends in climate. We had a cold December in North America because of an unusually strong La Nina effect bringing down Arctic air.

So temperatures are averaged, by day, by year, by decade, and across the globe – more than a thousand stations. That’s a lot of averaging. The public has to basically trust that the scientists are doing their jobs correctly, weeding out bias, and getting all the complex math right. Of course, no such project this massive will be without error and differing opinions about methods – so the scientific literature is full of articles on “unresolved issues” and conflicting data.

And in the end we have to trust scientists that they were able to detect a global warming trend of 1.5 degrees C since 1880, on the backdrop of all the local and short term fluctuations. I do trust the consensus (NASA can send out a probe and hit Saturn, so they have earned some trust) and I have not heard any arguments that I find compelling to distrust it. But I also understand why many in the public find it difficult to trust.

We also need to keep our logic clear. More often than not, when discussing the issue of climate change with a dissident, I hear arguments that essentially try to cast doubt on global warming by citing evidence of cooling that is either local or short term. This is reinforced by hard core doubters. For example, the Drudge Report (a conservative news aggregator) loves to run stories about how cold it is, and reveled in the fact that the Copenhagen summit was met by freezing temperatures (that may have had something to do with the fact that it was December in Copenhagen).

So let’s dispense with these arguments – there will be short term and local fluctuations in temperatures. There are many climate trends superimposed over each other. The claim of AGW scientists is that when you control for all known trends and fluctuations in climate, there is an extra warming trend of about 1.5 degrees C in the last century. This trend cannot be accounted for by any natural process, but can potentially be accounted for by forcing from greenhouse gases. That’s the claim – if you are going to doubt it, then at least address it – not some straw man about how cold it was in December, or the solar cycle, or some other trend that is already accounted for.

In the past climate science was an innocuous discipline, and the scientists fairly anonymous. Now they have been thrust into the middle of a raging political controversy, and big decisions are hinging on their data and analysis. I get the sense (reinforced by climategate) that the climatology community has not fully adapted to this reality. There is an opportunity now to accelerate this process. There needs to be more transparency in temperature data and its analysis, not because I think there is any fraud going on, but because we need transparency in order to have public confidence in the science.

Scientists may find it inconvenient and annoying, and would rather just limit their dealings to other scientists – but it’s too late for that. They have to learn how to deal with the public and with governments and politicians, and especially their critics, in an effective way. It’s not enough to have good science – society needs to trust it and make use of it.

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