Facts clear: Climate change exists

In my last column I answered the question "When it comes to the causes, extent and consequences of global climate change, should you rely on Fox News and tea partyers or climate scientists?" Does the question sound as absurd to you as it does to me?

It should, because to reject sound science and in its place accept ideologically or economically-based conclusions is dangerous folly. MIT climate scientist Kerry Emanuel, a conservative Republican, uses this issue as a litmus test before voting. Any candidate who rejects that humans are the primary cause of climate change lacks the intellectual capacity or honesty to earn Emanuel's vote.

Today, let's start to review the data for human-caused climate change, beginning with these facts: the planet's temperature has increased about 1.5 degrees F since 1880, when accurate measurements were first taken, and 2010 tied 2005 as the hottest year.

Because of the complexity of our climate system, regional temperatures may drop in the short term, even as global temperature rises. Thus, last year was only the 23rd warmest for the contiguous U.S., a fact that leads many Americans to the erroneous conclusion that the planet cannot be warming.

Projections for the 21st century are in the range of 3.2 degrees to 7.2 degrees F. Doesn't sound like much? A 3.6 degree increase makes the Earth as hot as it was during the mid-Pliocene, 3 million years ago. Incidentally, sea level was about 80 feet higher then than it is now.

Couldn't temperature increases of that magnitude be the natural result of hot-cold cycles? Not in this case. Here's why: The ultimate determinant of the Earth's temperature is its heat budget, the balance between solar radiation received (insolation) and that re-radiated back into space. When insolation is reduced, for example when the Earth is at a point in its orbit farthest away from the sun (which varies on a cycle of 100,000 years), the temperature is lower and an Ice Age may result. When insolation increases, temperature does as well and we may experience "hothouse" conditions.

Fluctuations due to variation in insolation - both past and future - are well understood. And we are currently in the midst of a period of decreasing insolation, a cooling phase. Thus, something is not only compensating for the slight cooling that should be happening, it is overwhelming it and heating the planet.

That "something" is an enhanced Greenhouse Effect, a physical phenomenon well-understood since the early 19th century, and one which you experience when the inside of your car is warmer than outside when you park it in direct sunlight.

Greenhouse gases that include water vapor, carbon dioxide, methane and nitrogen oxide act to trap heat in the atmosphere and thus prevent it from re-radiating back into space.

Water vapor is the most abundant greenhouse gas, but its role in climate change is subordinate to the other gases. After the planet has heated, water vapor increases in the atmosphere, and then it adds to global warming. The primary cause of climate change, of course, is increased levels of carbon dioxide due to burning fossil fuels and deforestation. Even though the atmospheric concentration of carbon dioxide is relatively low (392 parts per million), it is sufficient to heat the atmosphere.

In my next column, I'll present the remaining evidence, including the role of mathematical models. That done, it will be up to all of us to make pariahs out of those who reject sound climate science, to elect rational candidates who work in the public's and environment's interests, and finally, to act as if future generations and the planet matter.

Abel is a local college professor, environmentalist and author.