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Monday, August 29, 2005

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 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 24th 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:


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-14th to mid-19th century. However, there is evidence that solar radiation has actually been decreasing during the later half of the 20th 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.

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)…


T-Mac said...

Yea, cause is an objective source. Still, good start Jesse. Keep em coming.

Anonymous said...

I went to a seminar with a glaciologist (yes, a guy who studies glaciers and gets paid - life is sweet) and apparently the general consensus is that yes, the earth goes through (what we would consider) extreme temp. fluctuations every so many thousands of years - but that since evidence has been around those fluctuations have been continuing, but somewhat 'bumped' up since we got our hands on burning up resources. Whether this was another opinion or different interpretation of data - I cannot say.

Jesse Jenkins said...

Um... Tom, is the other guys (i.e. the skeptics). The whole point is that they are not very objective (their research is rarely peer-reviewed and is often funded by think tanks set up as fronts for the oil, coal and gas industries). is a site founded by climate scientists for debate of climate change issues and, while it adopts a climate change is happening view (not necessarily an indication of subjectivity, there is after all plenty of evidence for that conclusion), it accepts heated debate from experts in the field (check out the dozens of comments on each article they post). So, I'm not sure you really read the post closely or not but where exactly are you questioning the objectivity of my sources (most of them come from peer-reviewed articles - or summaries of them - in Science)?

Kristen, thanks for reading my blog. Yeah, as far as I've read, the earth goes through a lot of long term extreme temperature fluctuations,and the transitions between some can be relatively quick (for geologic time, like over 50 years or so), such as the beginning of the last major ice age. We also go through lots of shorter, less extreme fluctuations over decadal scales or even shorter ones (El Nino for example). These tend to create a fluctuating temperature record that looks kinda like a complicated sin-wave pattern. However, when you plot an average fit-line to that fluctuating pattern you can see, like you said, that it is getting "bumped up" in the last century. That is, while it still fluctuates around, it fluctuates around an increasingly high average point, indicating a larger warming trend.

Heiko said...

I think the scientific consensus frequently gets misrepresented.

What there is consensus on is indeed uncontroversial, that's why it's a consensus after all.

But there are many issues that are controversial, and they make the difference between relatively innocuous climate change where the costs of virtually all measures to combat it are nowhere near justifying the expense, and the apocalyptic scenarios being bandied about to pressure people into (expensive and misguided IMHO) action.

What isn't in dispute is:

1. We are emitting plenty of CO2
2. CO2 concentrations are steadily rising
3. CO2 is a greenhouse gas
4. Climate varies naturally

What there is some argument about is the relative magnitude of the man made and natural contributions,

and where the real beef is, is what policy measures can be justified.

My own opinion based on the IPCC assessment is:

Temperatures will rise by 2-3C by 2100, except if there are large emissions from coal after 2050. Whether those should happen is for policy makers after 2050 to decide, largely.

My personal opinion is that 2-3C and a doubling of CO2 concentrations will be a net positive for the planet, with reductions in heating requirements, extra agricultural output from CO2 fertilisation, more rain, and a reduction in temperature differentials between night and day, winter and summer and the poles and the equator, ie a milder Northern climate with fewer serious mid latitude storms, more than compensating for increased heat stress close to the equator, more flooding and probably somewhat more intense tropical storms.

And if the drawbacks should outweigh the benefits, I think they won't do so sufficiently so to justify expensive measures now.

If it's not truely catastrophy we are talking about, something in the direction of Venus, which is physically impossible,

then I also see a great benefit in waiting for technological change to make non carbon based energy sources so cheap that the problem solves itself at zero cost.

Why spend a few trillion now, when most of humanity is still dirt poor, to possibly in 50 or 100 years save a humanity that'll be richer on average than Americans are today trouble it will be easily able to deal with at any rate?

People don't worry about 0.6C+/-0.2C, moving from Boston to New York is in that ball park I should think.

They worry about the kinds of thing you cite, and that's where the scientific consensus gets abused horrendously.

Polar ice caps are thinning dramatically? The IPCC argues that the gains in Antarctica make up for losses elsewhere to a large degree. The reason is that Antarctica is so cold, ice accumulation there nearly entirely depends on precipitation, and in a warmer world with more evaporation, that precipitation is going up.

The majority of the sea level increase is actually due to thermal expansion.

And the word "dramatic" injects a false sense of speed. Air temperatures can change dramatically, ie by say 20 degrees C in a few hours, the oceans and ice have such a large heat capacity it takes forever and a day to melt them / heat them respectively (ie hundreds to thousands of years for Antarctica or Greenland to melt down).

The IPCC projection for sea level change is something like 8-80 cm by 2100, the higher end of the range again based on very large coal derived emissions after 2050.

So far, the evidence indicates little change in hurricanes, droughts, storms or flooding with decade spanning cycles absolutely overwhelming any underlying trend.

I am a scientist working on renewables, (fast pyrolysis of biomass), with my funding partially based on the perceived threat of climate change.

Problem is I just don't buy it. I think it's largely hype around a small kernel of truth, with lots of exageration to scare us.

And that opinion is widely shared among scientists.

Heiko said...

On storms there is a nice explanation above. Basically, global warming will reduce the poles equator temperature differential, and that ought to reduce mid latitude storms.

It will, however, slightly raise water temperatures in the tropics, and that ought to raise, if not the number, the intensity of tropical storms.

But, keep in mind these simulations are for much more global warming than has occurred so far.

The contribution so far is barely detectable in the data we've got.

Unfortunately the article doesn't state how much change is expected so far, but a not entirely scientific linear extrapolation based on temperature alone would reduce the half Sapphir Simpson Scale and 18% rain intensity increase to something like less than 5% for rain and maybe 4-5 mbar for pressure, and therefore maybe 4-5 miles per hour for windspeed.

So, ex climate change Katrina might have reached 170 miles per hour instead of 175, 906 mbar instead of 902 mbar and would still have been a category five storm.

Any conceivable reduction in carbon dioxide emissions we could have undertaken over the last decade would have a negligible impact, say the US had reduced emissions of CO2 by 1% per annum starting in 1990, I'd think the impact on Katrina of this would be well below 0.1 mbar and 0.1 miles per hour.