Climate Skeptics take note

For the tiny portion of the global population that still thinks that Global Warming is a hoax that Al Gore and some liberal scientists are proposing to make a few bucks, I swallow back some harsh words and will try to patiently offer some data for you to peruse. (I will try not to compare you directly to the idealists that still think that the reason that dinosaurs are buried deeper in the fossil record is because they had bigger shovels.)

First, to my friends that claim that the climate is now cooling, I ask you to explain the global instrumental temperature record below. Sure, I have chosen NASA’s record, but I could easily have chosen many others — some that show slightly more or less warming, depending on how exactly you calculate a globally-averaged annual temperature.

In 1991, we concluded that the 1980s were the warmest decade on record. In 2001, we concluded that the 1990s were the warmest decade in over 1000 years. Take a look at how the ’00s compared.

Note that while year-to-year temperatures fluctuate more wildly due to natural influences like El Niño and volcanic eruptions, the 5-year average tends to smooth these out. Also note that prior to the passage of the Clean Air Act in the 1970s, aerosols in the atmosphere (which block out sunlight) tended to mask much of the warming, and while you can see an upward trend, the natural cycles of climate still dominated much of the signal. Since the late 70s, the rise in temperature has been much steeper as the aerosols quickly fell out of the atmosphere and the greenhouse signal dominated.

This response is reflected not only in global temperatures (a pretty poor measure of climate, which includes all of the patterns of weather, not just averages and not just temperature), but we have seen reductions in northern hemisphere snow cover and Arctic sea-ice. See figure below from Post et al. (2009, Science 325, 1355, DOI: 10.1126/science.1173113).

One of the patterns that has long been expected from anthropogenic warming is enhanced warming in the polar regions. While we’ve barely felt the effects here in the mid-latitudes (where we are emitting the most carbon), the high-latitudes have been warming especially fast. It is no surprise that the Arctic has warmed (see below). What is surprising is how fast it has warmed, and how fast the Greenland Ice Sheet has responded to that warming.

This warming manifests not only in surface melt on the Greenland Ice Sheet, but a thinning of the ice and speeding up of outlet glaciers as they move toward the coast. Below is a map of this dynamical thinning derived from repeat laser altimetry. The blue circles (can you see them there??) are areas where the ice is actually thinning a bit. The red are areas that are thinning. The image comes from Pritchard et al. (2009, Nature, 10.1038/nature08471).

Gravimetric measurements of the ice sheet indicate that it is steadily losing mass, ending any debate as to whether mass loss on Greenland is outweighing the increases in accumulation that we expect in a warming climate.

Another surprise is how much the interior of Antarctica has warmed. 50 years of measurements reveal a robust warming trend on our southern-most continent.

Some of my less-informed acquaintances argue that the Earth is in a cooling trend and that it is all caused by solar radiation. And they are not altogether wrong. We should be in a cooling trend, were it only for natural forcings, like incoming solar radiation (or insolation, for short). The robust warming signal that we have witnessed in the last century puts an abrupt end to a long-term cooling trend in the Arctic. This figure is taken from Kaufman et al.(2009, Science 325, 1355, DOI: 10.1126/science.1173983).

So, while insolation in the Arctic is DECREASING, temperatures are INCREASING. This goes against all previous measurements and physics, unless you allow for a greenhouse warming (which is physically ubiquitous). Below, Kaufman et al. show that when insolation is low, temperatures are low. Except for now. Yes, human behavior is having a larger influence on climate than fluctuations in solar output.

So, what does this all mean? Many things. Two that I will share below. First, sea levels are rising. They are rising much faster than predicted. And they will continue to. We will likely see sea levels rise 1.2 m this century, more than they have fluctuated naturally over 2000 years.

And temperatures will continue to rise. There is no doubt about this. The question is whether we can keep temperature increases from exceeding the +2ºC critical limit (as is generally agreed upon as the “point of no return” in climate”). With extreme regulation measures, we MIGHT be able to. If we keep heading on our current path, there is no chance.

So, Rob, still thinking about taking that $10,000 bet?

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