I’m a biologist, and one of the things that biologists have been noting over that past several decades is the shifts in species’ ranges. Specifically, and particularly in the Northern Hemisphere (where most of the Earth’s land is – more on that later), the ranges of cold-adapted species have been shrinking while the ranges of species that tolerate warmer temperatures have been expanding northward and up into mountainous areas where they didn’t live just a century or so ago. I
have participated in research regarding the shrinking ranges of cold-tolerant species, by the way.
There’s no question that the amounts of greenhouse gases in the atmosphere are increasing. Nor is there any serious question that the Earth’s mean temperature is increasing. Unless the laws of physics were repealed when I wasn’t looking, increasing levels of methane and CO
2 in the atmosphere
must lead to a change in the Earth’s heat balance and a subsequent increase in the Earth’s mean temperature – unless the amount of sunlight reaching the Earth decreases to compensate. Besides, ice cores going back some 400,000 years demonstrate a close correlation between atmospheric CO
2 levels and mean global temperature.
There is, to be sure, often an apparent lag between a change in CO
2 levels and a change in mean global temperature. This is exactly what’s expected. The Earth is an enormous system and the oceans are a tremendous heat sink. It takes
time for a change in atmospheric CO
2 levels to change the heat balance of an entire planet. It’s also certainly true that other factors (Milankovitch Cycles, for instance) influence the planet’s climate, so it’s possible that rising CO
2 levels are sometimes a
response to rising global temperatures, rather than a direct cause.
Still, unless the physics of heat retention have changed, absent other changes (like, for example, a decrease in heat delivered to the Earth by the Sun), rising CO
2 levels
must cause the Earth’s temperature balance to shift upward.
The relevant questions are:
1.) “How much is the Earth’s mean temperature going to increase?”
2.) “How much of this is due to human activities?” and
3.) “What, if anything, can we/should we do about it?”
Here are some common claims of “Global Warming Skeptics,” with responses.
“There is no actual evidence of Global Warming. It’s just something that models predict.”
Untrue. That the planet’s mean temperature appears to be rising was noted well before there were models available that could make even the crudest approximations of the phenomenon.
The NASA Goddard Institute of Space Studies Surface Temperature Analysis (GISTEMP) is a measure of changing global surface temperatures using data from 1880 to the present. These data are not interpolations, but
direct measurements from weather stations scattered over the globe. The graph below is a summary of the data, showing how mean global temperatures have risen over the past 125 years.
This next graph shows the data broken down by region. Note that mean temperature change is highest at the highest latitudes (near the pole).
Satellite measurements also show the Earth’s average temperature is rising.
Glaciers all over the world are shrinking at a drastic rate. While it’s true that
some glaciers are still growing, that’s not surprising. All that’s necessary for a glacier to grow is that more snow falls in the winter than melts in the summer. So it’s unsurprising that some glaciers are still growing. But over the past century, the vast majority of the world’s glaciers that have been measured have been shrinking. This is a physical impossibility unless the climate has been warming.
Compare these two pictures, taken in Glacier Bay National Park. The first was taken on August 13, 1941. The second was taken August 31, 2004. The Muir Glacier (which was 2,000 feet thick in 1941) has retreated completely out of view.
The amount of sea ice in the Arctic Ocean has been declining for as long as the means have been available to measure its thickness and extent. The graph below shows the decline in sea ice from 1975 to the present. (Data from The National Snow and Ice Data Center, Boulder, Colorado.)
Since 1992, satellites have been measuring changes in mean sea level. As the oceans warm, they experience
thermal expansion. This graph shows changing sea levels around the world over the past decade or so. (Data from the National Oceanic and Atmospheric Administration.)
One particularly worrying trend is the melting of permafrost at Northern Latitudes. (This is where temperatures appear to be rising fastest.) Permafrost that has been in place for millennia is melting in Siberia, Alaska, and Northern Canada. As it does, it releases methane into the atmosphere, which is itself a greenhouse gas. This is a cause for considerable concern among atmospheric scientists.
There are several other lines of evidence showing that the Earth’s mean temperature is increasing (such as changes in nesting patterns of Northern-Hemisphere bird species, which nest several weeks earlier now than they did 100 years ago), but that’s sufficient for now.
“Global Warming is a hoax by left-wing environmental wackos.”
Here are a few “left-wing environmental groups” that have concluded that Global Warming is a real phenomenon, and that human activities are at least partially to blame.
The American Geophysical Union
The American Institute of Physics
The American Meteorological Society (AMS)
The Canadian Meteorological and Oceanographic Society (CMOS)
The Environmental Protection Agency
The Intergovernmental Panel on Climate Change (IPCC)
NASA's Goddard Institute of Space Studies (GISS)
The National Academy of Sciences (NAS)
The National Center for Atmospheric Research (NCAR)
The National Oceanic and Atmospheric Administration (NOAA)
The Royal Society of the UK (RS)
State of the Canadian Cryosphere (SOCC)
“The apparent rise in mean temperature is simply a result of the Urban ‘Heat Island’ Effect.”
Incorrect. Monitoring stations are often located well away from urban centers (atop remote mountain peaks, for instance), and the “heat island effect” is well understood and accounted for. In any event, independent measuring systems (e.g. satellites) confirm that the Earth’s mean temperature is rising.
“The current more or less universal agreement among atmospheric scientists that the Earth is warming is irrelevant, because in the 1970s, they were predicting ‘Global Cooling’.”
Incorrect. This is a myth that some GW “skeptics” continue to repeat even after its falsehood has been pointed out. There were some articles in
popular magazines which predicted “Global Cooling,” but this was mostly alarmist bunk by the media that was never supported by (and indeed, was debunked by) the general scientific community.
“Water vapor is the strongest Greenhouse Gas, and rising CO2 levels have nothing to do with mean global temperature.”
Incorrect. The reason climate scientists don’t waste time discussing changes in atmospheric water vapor levels (which is indeed a Greenhouse Gas) is because changing H
2O vapor levels are not a forcing agent like changing CO
2 levels are. The amount of H
2O vapor in the air is a
function of temperature change, not a
cause.
If you could magically remove all the CO
2 from the atmosphere, the planet’s temperature would begin to fall. As it fell, water vapor would condense and rain out of the atmosphere. As the planet continued to cool, water vapor that hadn’t rained out would freeze out as snow, until there was little or no water vapor left. At that point, the planet’s average temperature would be well below freezing.
That’s why the driest place on Earth isn’t the Sahara or the Gobi Desert, it’s Antarctica. Despite that fact that it is a Greenhouse Gas, the concentration of water vapor in the atmosphere is a very sensitive
result of temperature, not a
cause of it.
“Rising mean global temperatures are due to natural cycles. Human activities have nothing to do with it.”
It’s certainly true that the planet’s mean temperature has fluctuated over time, and it will continue to do so in the future, whether humans are around or not. Much of the current rise in mean global temperature may indeed be completely independent of human activities.
But GW “skeptics” who insist that human activities have nothing to do with the planet’s mean temperature must explain the magical process by which you can increase the amount of CO
2 in the atmosphere by 30% and
not cause the Earth’s heat balance to shift upward.
“Volcanoes emit more CO2 than do human activities, so anthropogenic CO2 is irrelevant to Global Warming.”
I
really dislike this one, because it’s an outright lie. Human activities contribute an estimated 150 times as much CO
2 to the atmosphere as do volcanoes. This is readily apparent to anyone who bothers to look at the atmospheric CO
2 data. If volcanoes were a significant source of atmospheric CO
2, you’d see a sudden “spike” in atmospheric CO
2 every time there was a major volcanic eruption. This doesn’t happen.
“Satellite observations show that the Earth is cooling, not warming.”
Another outright lie. It’s true that
one analysis of satellite data showed tropospheric cooling, but those measurements were shown to be in error and have since been corrected. Other satellites have consistently shown the Earth to be warming.
“Natural emissions of CO2 into the atmosphere dwarf human emissions. So Global Warming isn’t anthropogenic, even if it’s caused by CO2 emissions.”
It’s true that natural emissions of CO
2 (decay of plant matter, respiration by animals, etc.) are something like 30 times that of anthropogenic CO
2 emissions.
But, respiration (which adds CO
2 to the atmosphere) and photosynthesis (which removes CO
2 from the atmosphere) are tightly linked and essentially balanced. For the past 10,000 years or so, for every ton of CO
2 put into the air by “natural” processes, a ton was removed by photosynthesis and absorption by carbonates. So, atmospheric CO
2 levels remained more or less in balance.
The difference nowadays is that human activities add something like 6
billion tons of CO
2 to the atmosphere each year, but we don’t
remove the CO
2 that we contribute, unlike natural processes. Fortunately, about half of that 6 billion tons
is absorbed by the oceans. But that still means that the amount of CO
2 in the atmosphere increases by about 3 billion tons per year.
“Some places are cooling, not warming. This shows that Global Warming is a myth.”
While it’s true that some parts of the globe are cooling right now instead of warming, this in no way refutes the conclusion that the Earth’s
average temperature is increasing. Indeed, increasing average temperatures are expected to cause changes in atmospheric and oceanic currents that distribute heat, leading some places to become
cooler (at least in the short term) even as the planet’s average temperature increases.
Saying that because
some parts of the globe are getting cooler, the planet as a whole cannot be warming is like claiming that because it’s
sometimes true that a day in February is warmer than a day in June, June is not a warmer month on average than is February. [This assumes you live in the Northern Hemisphere.]
Well, there’s lots more to this subject, but this is all I have time for right now.
Cheers,
Michael
Global warming
Fruitcake Fringe has posted a couple of news items relating to the subject. If you're not a member of the 
.
Linear Mode
