Evidence for climate change is irrefutable and we need to address it

After record-breaking snowfall in Washington and Virginia, many water-cooler conversations began with "What global warming?" The East Anglia debacle did not help. But global warming is real, and this is a retelling of an "inconvenient truth."

Global warming refers to the increase in the average temperature of Earth's near-surface air and oceans during the 20th century and, more ominously, its projected continuation. What has happened up until now is irrefutable. Measurements coupled with sophisticated analysis to glean trends from random daily and seasonal variations indicate that the global temperature increased 0.74 degree Celsius between the start and end of the 20th century; the last decade was the warmest on record.

But will the trend continue for the next 100 years? And is it human-caused or part of a natural cycle that has existed since the Earth formed 4.5 billion years ago? The answers are: yes and yes.

Less than 1 degree temperature rise per century seems innocuous. But a couple more degrees and ice in the Arctic and Antarctica melts, sea level rises, coastal cities disappear, and desertification spreads. Even if the looming catastrophe were not human-caused, the only species capable of slowing the trend should tackle the problem aggressively, whatever the sacrifice.

Scientists employ the laws of nature as they understand them; by solving resulting dynamical equations, the future can be predicted. For the case of planetary orbits around the sun, the equations can be solved to a high degree of precision, and humans have been able to predict eclipses of the sun and moon, ocean tides and other phenomena dependent upon those orbits.

Unfortunately, equations to predict average temperatures are much more complicated, and even the fastest computer cannot give precise answers in a reasonable time. So, scientists simplify the laws of nature using heuristic models, so supercomputers can provide answers. The reliability diminishes as the degree of simplification increases. Climate change over a decade is less reliable than the weather forecast for the next three days.

Predictions are made statistically; for example, if trends continue, there is a 25 percent probability warming over the next 25 years will exceed 2 degrees Celsius. Certainty is replaced by likelihood.

Nevertheless, short-term weather forecasts and long-term climate predictions are good. The accelerated Earth warming predicted in 1990 was on the mark when 2000 and 2010 rolled along. In fact, summertime melting of Arctic sea ice has accelerated far beyond expectations. Also, climate models predict increased severity and frequency of hot and cold weather events.

This puts to rest the sneering each time a cold wave or snowstorm hits. Broadcasters Rush Limbaugh and Matt Drudge, and Sen. Jim Inhofe, R--Okla., are no more right about a single snow event (or two or three) proving global cooling than lack of snow in Vancouver confirms global warming.

Dismissing the science because of its inability to provide certainty but rather likelihood is playing Russian roulette with the health and prosperity of future generations.

Confidence in existing models to make predictions settles the question of whether warming trends will continue. But what is causing global warming? There is evidence it is part of a natural cycle, but is this trend exacerbated by human activities?

Ice or glacial ages occur on Earth quasi-periodically over millions of years. Within a long-term ice age, short-term pulses of extremely cold (glacial periods) and warmth (interglacial periods) occur, also quasi-periodically, but over tens of thousand of years. Earth has been experiencing an ice age for 2.588 million years, with the peak of the last glacial period 20,000 years ago.

Earth has been in an interglacial period, or natural warming period, for 10,000 years, and for most of those years humans have had insignificant influence on the rate of warming.

Among the hypothesized causes for the natural cycles are atmospheric composition, cyclical changes in Earth's orbit and motion of tectonic plates. Greenhouse gases -- such as water vapor, carbon dioxide, methane and ozone -- contribute to global warming when released into the atmosphere in quantities beyond a delicate balance: Less than that balance and cooling ensues; more results in warming. Carbon dioxide is released as a result of animal metabolism, volcanic eruptions and forest fires. The same gas is absorbed by the oceans and rain forests.

But the natural global warming that started 10,000 years ago has accelerated since the start of the industrial revolution, when fossil fuels increasingly began to supply our energy needs. The sudden global warming correlates strongly with the increased release of human-caused carbon dioxide and, to a lesser extent, other greenhouse gases such as nitrous oxide and chlorofluorocarbons.

Climate models that take into account fossil-fuel usage and production of carbon dioxide have consistently and correctly predicted an increase in surface temperature beyond that of the interglacial period alone.

Science works via a system of checks and balances of peer review, empirical validation and independent reproducibility. Some scientists fabricate, cherry-pick or embellish data; are biased by certain preconceived ideas; or simply make mistakes. But those are few and far between, and the system is designed to expose the charlatans, the misguided and the foolish.

Relative to global warming is "Climategate": More than 1,000 e--mails were hacked and released from the servers of the University of East Anglia in the United Kingdom. The messages hint at manipulation and selective destruction of data to bolster the case for human-accelerated global warming. An inquiry is being conducted there and another was just completed at Penn State University (at the other end of many of these e-mails).

There is damage to the case of anthropogenic global warming, but it appears that this episode does not rise to a level of dishonesty or misconduct, but rather sloppiness and overzealousness with unofficial, nonjournal writings. Archival evidence from many other researchers for human-caused global warming still stands high.

So, for the foreseeable future, Homo sapiens need to conserve energy, seek alternatives to fossil fuels, control population growth, and provide sustainable balance to our home's delicate ecosystem.

Gad-el-Hak is the Inez Caudill eminent professor of mechanical engineering at Virginia Commonwealth University.