A Washington Times editorial falsely suggested global warming science is undermined by studies indicating that the planet, at least in some regions, saw exceptional warmth thousands of years ago. But climate experts don't dispute that certain regions have experienced natural warm and cool periods throughout history; they say climate change of the past half century is "different" because it can't be explained by "natural changes alone."
Wash. Times suggests study undermines human-caused global warming
Editorial: Claims by "alarmists" about global warming and temperature "neither fit with the historical record nor with a growing body of scientific evidence." A May 19 Washington Times editorial claimed:
The planet has never been warmer than it is right now, if you believe what global warming alarmists have to say. Mankind's selfishness in producing "excessive" amounts of carbon dioxide has set us on a path toward global cataclysm, they insist. The problem with this tale is that it neither fits with the historical record nor with a growing body of scientific evidence.
Editorial cites study of regional temperatures over two millennia. As evidence, the editorial cited a recent study of mollusk shells in Iceland published in the Proceedings of the National Academy of Sciences. The study found "significant variation in seasonal temperature over the period from ~360 B.C. to ~A.D. 1660" and that "reconstructed water temperatures for the Roman Warm Period in Iceland are higher than any temperatures recorded in modern times." The editorial concluded:
These facts will not sit well with the climate-change theocracy. In order to sell the notion that global warming is a consequence of industrialized society, the fundamental article of the warmist faith must be that modern times are the hottest on record. Much like the ancient Romans, today's environmentalists believe extreme weather conditions are not a phenomenon with natural causes, but rather a portent of Mother Earth's displeasure with the choices made by the people.
Other studies from around the world confirm the existence of Roman and Medieval warming periods, where no source of "greenhouse gases" existed aside from the horses and cows of the time. For that reason, we encourage our senators to stab their daggers into the heart of cap-and-trade and all other legislation being promoted in the name of climate-change fiction.
IPCC: "[P]ast climate changes were natural in origin ... whereas most of the warming of the past 50 years is attributable to human activities." In its 2007 assessment report, the Intergovernmental Panel on Climate Change stated that "[c]limate has changed on all time scales throughout Earth's history," but that "[t]he concentration of CO2 in the atmosphere has reached a record high relative to more than the past half-million years, and has done so at an exceptionally fast rate. Current global temperatures are warmer than they have ever been during at least the past five centuries, probably even for more than a millennium." It added, "Another unusual aspect of recent climate change is its cause: past climate changes were natural in origin ... whereas most of the warming of the past 50 years is attributable to human activities."
IPCC: "The fact that natural factors caused climate changes in the past does not mean that the current climate change is natural." The report also states that past changes were most likely due to the sun's effects on the Earth and that "[t]he fact that natural factors caused climate changes in the past does not mean that the current climate change is natural." From the report:
Another likely cause of past climatic changes is variations in the energy output of the Sun. Measurements over recent decades show that the solar output varies slightly (by close to 0.1%) in an 11-year cycle. Sunspot observations (going back to the 17th century), as well as data from isotopes generated by cosmic radiation, provide evidence for longer-term changes in solar activity. Data correlation and model simulations indicate that solar variability and volcanic activity are likely to be leading reasons for climate variations during the past millennium, before the start of the industrial era.
These examples illustrate that different climate changes in the past had different causes. The fact that natural factors caused climate changes in the past does not mean that the current climate change is natural. By analogy, the fact that forest fires have long been caused naturally by lightning strikes does not mean that fires cannot also be caused by a careless camper.
UK Met chief scientist: Today's warming is "very different" from previous warming. Julia Slingo, the chief scientist at the U.K. Met Office, has explained that "it's right that the climate does have natural variations on all sorts of time scales, from year to year associated with things like El Niño ... to longer timescales and even things like the variations that we see in the record around the middle ice age, medieval warm period, they are all parts of natural variability of the climate system." Slingo further said climate observations indicate that current changes are "not the same as the natural variations that we've seen in the past":
But what we're finding now is that the fingerprint as we might call it of global warming, looks very different if we look at it not just in terms of surface temperature but if we look at it in terms of the temperature changes throughout the atmosphere, through changes in rainfall patterns, through changes in how much water the atmosphere is holding, all those things are the fingerprints which tell us this is not the same as the natural variations that we've seen in the past.
Even if we go back to the big gyrations that the climate of the planet has gone through in the ice ages as I've already discussed, those are not the same as the ones we are seeing now and in particular the rate of warming is far more rapid then we have ever seen in any of those records of glacial and interglacial cycles, so our planet is changing at an unprecedented rate and that, again, is not consistent with natural cycles within the climate system.
Slingo noted that CO2 emissions are "enhancing that greenhouse effect and leading to an increase in temperature." Slingo also said:
What carbon dioxide is doing now is enhancing that greenhouse gas effect. So we understand the basic physics of that. It's enhancing that greenhouse effect and leading to an increase in temperature, so we're trapping more energy into the planet because of increasing levels of carbon dioxide.
How do we know that it matters? Well you don't have to really think to hard that if you've gone from before we started our industrial activities in the 19th century, carbon dioxide levels were at 280 parts per million by volume. We are now rapidly approaching 390 parts per million which means it's been a 40% increase. Most of that increase has happened in the last 50 years. And if we know that carbon dioxide is a greenhouse gas, it's hard to believe that if you increase it by 40% you're not going to do something to the temperature of the planet.
New Scientist: "Many studies suggest" current warming "can only be explained by taking into account human activity." New Scientist magazine reported in 2007 that "[i]t is certainly true that Earth has experienced some extremes that were warmer than today, as well as much colder periods," but that we "cannot dismiss" current warming "as natural variation just because the planet has been warmer at various times in the past. Many studies suggest it can only be explained by taking into account human activity":
It is certainly true that Earth has experienced some extremes that were warmer than today, as well as much colder periods. In some cases the main factors that caused these past warm periods -- and the ebb and flow of ice ages over recent millennia -- are well understood, though not in all. Many of the details remain unknown.
The important question is what is causing the current, rapid warming? We cannot dismiss it as natural variation just because the planet has been warmer at various times in the past. Many studies suggest it can only be explained by taking into account human activity.
Nor does the fact that it has been warmer in the past mean that future warming is nothing to worry about. The sea level has been tens of metres higher during past warm periods, enough to submerge most major cities around the world.
Climate Change Resource Center: Climate models "cannot capture the rapid increase in global temperature of the past half century without including greenhouse gas forcing." The U.S.. Department of Agriculture's Climate Change Resource Center states:
Q: If climate varied naturally in the past, how do we know that humans are disrupting climate now?
A: General Circulation Models (GCM) of the atmosphere are now being coupled with those of the oceans (AOGCM), ice, and the Earth's terrestrial biosphere. These models have been under development for many decades. They spontaneously exhibit interannual and interdecadal oscillations not unlike those observed in the real Earth System. They are run under different starting conditions and using different amounts of solar, volcanic, and greenhouse gas "forcing" of the atmospheric dynamics. Using this "ensemble" approach, various AOGCMs have successfully simulated the Earth's climate over the past 1,000 years. However, they cannot capture the rapid increase in global temperature of the past half century without including greenhouse gas forcing (IPCC 2007). Similarly, the models are able to simulate the warming of the upper 700 meters of all the major oceans of the world over the past 40 years, but only if they include the greenhouse gas emissions of the industrial age (IPCC 2007).
Pew Center on Global Climate Change: "[N]atural climate variability can be distinguished from human-caused climate change." The Pew Center on Global Climate Change states, "Climate varies naturally over both short and long time-scales, but natural climate variability can be distinguished from human-caused climate change." The Pew Center also states:
Scientists have conducted a number of attribution studies that compare observed changes in the global climate with those factors that are known to influence climate. These studies indicate that the climate change observed over the 20th century is due to a combination of changes in solar radiation, volcanic activity, land-use change, and increases in atmospheric greenhouse gases. Of these, greenhouse gases appear to be the dominant driver of climate change over the past few decades.
UCS: "Natural changes alone can't explain the temperature changes we've seen." According to the Union of Concerned Scientists:
Natural changes alone can't explain the temperature changes we've seen. For a computer model to accurately project the future climate, scientists must first ensure that it accurately reproduces observed temperature changes. When the models include only recorded natural climate drivers -- such as the sun's intensity -- the models cannot accurately reproduce the observed warming of the past half century. When human-induced climate drivers are also included in the models, then they accurately capture recent temperature increases in the atmosphere and in the oceans. When all the natural and human-induced climate drivers are compared to one another, the dramatic accumulation of carbon from human sources is by far the largest climate change driver over the past half century.