Please read the whole article at the source. There’s a lot more detail, diagrams, pictures, and basically just a lot to learn there. The excerpts below are just a few highlights I snipped out.
Global Warming and Nature’s Thermostat
by Roy W. Spencer
Roy W. Spencer received his PhD in meteorology at the University of Wisconsin-Madison in 1981. He has been a Principal Research Scientist at the University of Alabama in Huntsville since 2001, before which we was a Senior Scientist for Climate Studies at NASA’s Marshall Space Flight Center where he received NASA’s Exceptional Scientific Achievement Medal. Dr. Spencer is the U.S. Science Team leader for the Advanced Microwave Scanning Radiometer flying on NASA’s Aqua satellite. His research has been entirely supported by U.S. government agencies: NASA, NOAA, and DOE.
A Summary, and the Future
It is now reasonably certain that changes in solar radiation cause temperature changes on Earth — for instance, the 1991 eruption of Mt. Pinatubo caused a 2% to 4% reduction in sunlight, resulting in two years of below normal temperatures. It is not so obvious, however, that small changes in the Earth’s infrared cooling from mankind’s burning of fossil fuels will do the same. This is because the Earth’s natural greenhouse effect is mostly under the control of weather systems: specifically, precipitation systems. Either directly or indirectly, these systems determine the moisture (water vapor and cloud) characteristics for most of the rest of the atmosphere.
Precipitation systems thus act as a thermostat, causing cooling when temperatures get too high (and warming when temperatures get too low). It is amazing to think that the ways in which tiny water droplets and ice particles combine in clouds to form rain and snow could determine the course of global warming, but this might well be the case.
I believe that it is the inadequate handling of precipitation systems — specifically, how they adjust atmospheric moisture contents during changes in temperature — that is the reason for climate model predictions of excessive warming from increasing greenhouse gas emissions.
I predict that further research will reveal some other cause for the warming we have experienced since the 1970’s — for instance, a change in some feature of the sun’s activity. In the meantime, a high priority research effort should be the study of changes in precipitation systems with changes in temperature — especially how they confer moisture charateristics to the atmosphere as air is continuously recycled through them.
Fortunately, we now have several NASA satellites in Earth orbit that are gathering information that will be immensely valuable for determining how the Earth’s climate system adjusts during natural temperature fluctuations. It is through these satellite measurements of temperature, solar and infrared radiation, clouds, and precipitation that we will be able to test and improve the climate models, which will then hopefully lead to more confident predictions of global warming.
Warming Over the Last Century
There is little doubt that globally averaged temperatures are unusually warm today (at this writing, 2007). While a majority of climate researchers believe that this warmth is mostly (or completely) due to the activities of mankind, this is as much a statement of faith as it is science. For in order to come to such a conclusion, we would need to know how much of the temperature increase we’ve seen since the 1800’s is natural.
Warming Over the Last Millenium
Thus, at least in the context of the last century or more, today’s global temperatures are unusually warm. But when was the last time that the Earth was this warm?. You might have heard claims in the news that we are warmer now than anytime in the last 1,000 years. This claim is based upon the “Hockey Stick” temperature curve (Fig. 2) which used temperature ‘proxies’, mostly tree rings, to reconstruct a multi-century temperature record. That “warmest in 1,000 years” claim lost much of its support, however, when a National Acadamy of Science review panel concluded in 2006 that the most that can be said with any confidence is that the Earth is warmer now than anytime in the last 400 years. (Note that this is a good thing, since most of those 400 years occurred during the Little ice Age.)
But it turns out we don’t need to use “proxies” for temperature like tree ring measurements — there are actual temperature ‘measurements’ that go back over 1,000 years. ‘Borehole’ temperatures are taken deep in the ground, where the seasonal cycle in surface temperature sends an annual temperature “pulse” down into the Earth. A measurement and dating of these pulses from Greenland (Fig. 3) reveals much warmer temperatures 1,000 years ago than today.
Note that such methods for dating temperatures cause a “smearing” of the signal in time. Because of this smearing effect, decadal-time scale temperature “spikes” probably occurred during the MWP which are smoothed out in Fig. 3. If we could see those temperature spikes that undoubtedly occurred during the MWP, our current warmth would seem even less significant.
Thus, we see that substantial natural variations in temperature can, and do, occur — which should be no surprise. So, is it possible that much of the warming we have seen since the 1970’s is due to natural processes that we do not yet fully understand? I believe so. To believe that all of today’s warmth can be blamed on manmade pollution is a statement of faith that assumes the role of natural variations in the climate system is small or nonexistent.