The Case for Climate Change Part 1

This is the first of what will likely be four posts on the global climate change debate. After writing a couple of posts that called for small personal actions to combat global climate change, I received a bit of skepticism from some of you. They raised a number of key questions that I will hope to address in this and subsequent posts. They are the following:

1) Is the earth in fact getting warmer? And if it is, is it simply a cyclical occurrence or something more drastic?

2) If it is getting warmer, are human activities the cause? If so, what ones? (We're going to need to know which activities to curtail for step 4).

3) If it is getting warmer, is it necessarily a bad thing? What are the consequences and costs? (We're going to need to know the consequences to do step 4)

4) If it does exist and is bad (i.e. has costs), what actions can we take and will their costs be justified?

Before we begin with the first question, a bit of a caveat is required: I am not a scientist. I am not trained in any scientific field beyond a general knowledge of physics, chemistry and biology. I am an undergraduate student and my areas of interest and study are energy, computer science and philosophy. This is to say, take my words with a grain of salt. Smarter experts than me have tackled this issue and I suggest that you go read them for yourself: to read experts tackling some of the same questions, download the free pdf of the National Academy of Science’s report, Climate Change Science: An Analysis of Some Key Questions here; for ongoing discussion of climate change, check out the definitive climate change blog RealClimate.

What follows is an attempt by a reasonably intelligent individual to sort out some of the contentious areas surrounding the global climate change debate and present my conclusions in a manner that other reasonably intelligent individuals can understand. As I research this topic, I come to find more and more how complicated climate science is. This is an area where some controversy still exists and some of it is with good reason. A lot of work has been done in recent years to develop climate science and our understanding of climate records and current climate events have become pretty solid. However much more needs to be done in the near future to develop climate science’s predictive capabilities so that we can better understand the potentially dire consequences global climate change can bring.

I’d also like to suggest a couple of primers on climate change if you are interested. The Wikipedia climate change entry and global warming entry are both pretty good and provide lots of links to ancillary issues (thanks Wikipedia!).

Finally, why bother with these posts at all. Isn’t there a consensus on the issue of global climate change? Well, that is an interesting question in itself. Some object (quite loudly) that there is any kind of consensus on this issue. So, just how controversial is global warming now days?

Well, the short answer is: not very (see here for more). A key factor in judging when scientific consensus has occurred is the status of the debate in peer-reviewed scientific journals. A recent article published in Science surveyed 928 articles on climate change objectively selected from peer-reviewed journals (based on the key words “global climate change” in their abstracts). It revealed that ALL of the articles not only support the consensus that global climate change IS occurring, but also that it is likely being caused by human activity. Now, it is possible that some dissenting opinions were missed in the survey but the fact that none turned up indicates that the number of credible objectors to climate change is in fact very small. Sufficient evidence has also been presented to convince the UN’s Intergovernmental Panel on Climate Change (IPCC), the American Academy of Sciences, the American Meteorological Society, the American Geophysical Union, the American Association for the Advancement of Science, as well as the national sciences academies of all the G8 nations as well as India, China and Brazil and of course the governments of over 150 signatories to the Kyoto Protocol. Even George W Bush has finally come around (see The Guardian here). All this of course constitutes an appeal to authority. It is, however, a very convincing one!

What seems to have happened is that a few very vocal opponents (many of whom are receive funds from oil gas and coal companies and very few of whom submit their writings for peer review) have created an impression that there is little consensus (see Global Warming.org for a good example of the skeptic viewpoint and here for a list of key climate change skeptics – Oregon’s own official weatherman, state climatologist George Taylor of OSU is a vocal skeptic; see Willamette Week’s August 24^th cover story for more). Much of their objections, as we will see, are either relatively old (i.e. from the period of heightened global warming debate surrounding the Kyoto Protocol, roughly 1998-2001) and have been largely put to rest in the intervening time or are based on very narrow subsets of the available data.

So if you are the type of person to accept consensus opinions of well informed experts, you can stop reading now. Rest assured that global climate change is occurring, is likely caused by humans and that something had better be done about it soon (like yesterday people!).

However, if you, like me, would rather see the arguments for yourself, read what follows and use it as a starting point for your own investigation of this matter. A few key objections do still exist and issues do become more controversial as we progress in our four questions. It is these objections that I hope to discuss and address in this series of posts.

So, onto my take on climate change; we’ll start with these questions:

1) Is the earth in fact getting warmer? And if it is, is it simply a cyclical occurrence or something more drastic?

We begin with the least controversial of the four questions. Temperature data for the past 1000 years shows that global average sea surface and land air temperatures showed a slight general cooling trend (with smaller fluctuation periods) until a relatively rapid increase of .6 C (+/- .2 C) during the 20th century, much of it in the last few decades. This increase is likely the largest in any century for the past millennium. This warming trend is spatially widespread but temperatures trends do vary across different regions with the arctic North seeing drastic average warming of up to 7 C (12.6 F) for example and other regions seeing an overall cooling trend. Furthermore, the Northern hemisphere has seen more warming than the South. This is why, as my beautiful and intelligent girlfriend thankfully reminds me, the term ‘global warming’ is not truly accurate and why ‘global climate change’ is a more accurate term (this is the term I use throughout this post).

So where do these temperatures come from? The global temperature record comes from a compilation of sources: satellite records begin around 1979 and radiosonde weather balloon data exists from 1958 onward; thermometer readings from land and ships have been reliably collected from about 1850 onward; for the period before this, methods for determining temperature from proxies (i.e. relative concentrations of H2O-16 and H2O-18 isotopes in ice or mud core samples, width of tree rings etc.). These measured temperature trends are supported by a number of secondary observable (and alarming) trends such as widespread coral bleaching, rapidly receding high altitude glaciers, melting polar ice and arctic permafrost, decreased snow cover, increases in average sea levels as well as a number of other temperature linked events. Current trends indicate a dramatic rise of between 1.9 and 5.8 C (3.42 to 15.84 F) in the next century. This being said, there are still a few objections to the general consensus that the earth is warming at an unusual rate:

Objections:

1- The surface temperature data is skewed by the Urban Heat Island (UHI) or Asphalt Zone Effect.

-The UHI effect is a well-documented occurrence. Urbanization and the increase in highly heat-absorbent (low-albedo) asphalt, buildings and other manmade materials coupled with decreases in cooling evaporation from trees and plants causes increased temperatures in built-over areas like large cities and metropolitan areas. On hot days, the UHI can increase urban temperatures by 2-10 F compared with surrounding areas. The UHI also causes changes in precipitation patterns (monthly rainfall is about 28% greater between 20-40 miles downwind of cities, compared with upwind).

Some skeptics of global warming have pointed out the fact that some of the temperature measurements that make up the global temperature record are made within urban areas and that these measurements are likely skewed by the UHI. They use this fact to question the validity of the surface temperature record. Urbanization has rapidly increased since the industrial revolution, and thus a resulting increase in the surface temperature record could be expected, their argument goes. Warming trends are thus due not to real global warming but to the UHI skewing the surface record.

However, the UHI has been well documented for decades and its effect on the surface temp record has been taken into account. The UHI does not affect rural temperature readings or sea surface temperature measurements. The UHI can thus be cancelled out by comparing trends in urban data with trends in nearby rural or ocean areas to isolate and remove its effect. This method has been quite accurate in North America and Europe where many sampling sites are close enough for this to work (and also where the UHI is most pronounced due to large-scale urbanization) but gets less reliable in the Tropics (where sample sites are farther apart). Furthermore, peer-reviewed studies have been published (see Thomas C Peterson, 2003, ppt version at here) that contend that the effect of the UHI on the surface temp record is negligible, even without compensation (if this is the case, then records that have been compensated for UHI are too low).

2- Troposheric temperature records from weather balloons (radiosondes) and satellites (Microwave Sounding Units or MSUs) do not indicate the increase in temperatures that the surface records do, invalidating the surface record (the two agree so the third must be incorrect see here for example).

-This apparent contradiction between temperature records has provided major ammunition for global climate change skeptics. However, it has largely been refuted. First of all, it must be noted that satellites are regularly adjusted using data from radiosondes, so the two records are really more like one interrelated record.

Furthermore, the radiosonde data from weather balloons has numerous well documented flaws. Balloon instrumentation and data processing methods have changed frequently over the years and have resulted in discontinuities in these temperature records. Additionally, complicated systems are used to correct for various inherent flaws in radiosonde data. Three reports published in Science just this month (see here and here for a discussion of the articles on RealClimate) found that flaws in these correction methods caused errors that when rectified bring the radiosonde temperature record more in line with the surface record and climate models. Sherwood et al. for example found that methods used to counteract solar heating issues resulted in -.16 C per decade trend, masking the true warming. Radiosondes are designed to collect data on short term trends, not long term trends like climate change. They can thus be forgiven for some of their flaws but nonetheless, these flaws must be taken into account.

Similar overcorrection issues arise with the satellite record (especially because the often rely on radiosondes for calibration, as mentioned above). A recent revision (version 5.2) of one of two main interpretations of satellite records, the UAH record (University of Alabama Hunstville), thus shows a 40% higher per decade warming trend than the previous version. This reflects the work of Mears, et al. (also featured in the Science article mentioned above) which involved diurnal correction methods – i.e. methods for correcting daily variations in temperatures. Thus, while skeptics latch on to the old satellite record which showed only a .04 C per decade warming trend in the atmosphere contradicting the .17 C per decade surface temperature warming trend, the most recent satellite trends show .051 per decade for UAH and .134 C/decade from the RSS (Remote Sensing Systems) interpretation. Furthermore, the UAH record has been increasingly revised upwards in recent years, due both to recently revealed flaws (as described above) and to higher temperatures recorded in recent years. This may indicate that there is some lag time between surface trends and atmospheric trends which could account for the remaining discrepancy.

Perhaps the most critical argument against skeptics who tout the atmospheric record as proof that global warming isn’t occurring is that even if the atmospheric temps were accurate and the atmosphere was in fact not warming as quickly as the surface record indicates, this still does nothing to refute the surface temperature record. As the National Research Council concluded after reviewing the satellite records:

The warming trend in global-mean surface temperature observations during the past 20 years is undoubtedly real and is substantially greater than the average rate of warming during the twentieth century. The disparity between surface and upper air trends in no way invalidates the conclusion that surface temperature has been rising.

Saying that the troposphere isn’t warming does little to explain the rapid melting of polar ice caps, tundra permafrost and high altitude glaciers worldwide, nor does it disprove the surface record. At the most, it shows that our atmospheric climate models need some work and we don’t understand fully how surface and atmospheric trends interact.

3- "Climate change" is just a cyclical occurrence, a warming trend caused by the varying El Nino effects or fluctuations in solar radiation.

-It has been consistently shown that various natural climate fluctuations cannot account for the recent warming trends. El Nino/La Nina cycles are too short term and do little to explain long term trends.

Opponents frequently point to natural fluctuations in solar radiation as a key driver of variations in temperature. Indeed, climatologists generally agree that solar fluctuation has been key in driving global climate change trends in the past including the “Little Ice Age,” the widespread cooling trend that occurred in the Northern Hemisphere from roughly the mid-14^th to mid-19^th century. However, there is evidence that solar radiation has actually been decreasing during the later half of the 20^th century, resulting in what some call a “global dimming." This would indicate that global warming trends have actually been underestimated – i.e. anthropogenic causes have not only increased average temps but have done so while counteracting natural decreases in solar radiation.

Conclusions:
So, my in no way exhuastive study of the arguments surrounding whether or not an increase in global temperatures is occuring indicates that it seems safe to conclude that global temperatures have truly increased over the past century. The exact degree of increase is still open to debate (even the IPCC’s figure of .6 C includes a margin of error of +/- .2 C) but arguments about the Urban Heat Island, discrepancies with troposphere temperature records or alternative explanations like variations in solar radiation do little to counter the growing evidence for global climate change. Like we really needed thermometers to tell us what we could already clearly see all around us: polar ice caps have thinned dramatically, glaciers have retreated to heights never before reached this millennium, sea levels have risen measurably, the frequency of major weather events like hurricanes and drought is becoming more severe and Arctic permafrost is thawing for the first time since the last major Ice Age, threatening to release thousands of tons of methane into the atmosphere.

Next time, we’ll look at whether or not human activity is the cause of all this warming. Stay tuned (no guarantees on when Ill be able to get it written)…