I was recently in a conversation with someone who suggested that this winter's heavy snows in the eastern U.S. had "proved Al Gore wrong" or words to that effect. The person who said this isn't especially interested in science but is not at all dumb, and the idea is probably fairly commonplace. In fact, a couple of weeks ago Senator James Inhofe (R-Oklahoma) brought a snowball to the Senate floor to make the same point. He was widely mocked for doing so, but I don't recall anyone taking time to say actually why the notion is misguided (aside from pointing out that other parts of the U.S. have been unusually warm this year, and the most recent winter is probably the hottest on record globally).
So I thought I'd try my hand at a very brief explanation.
To start with, "global warming" doesn't mean the globe is warm, only that the average global temperature is rising. Over the past 250 years the Earth's temperature has risen about 1.4 degrees Celsius (2.5 Fahrenheit). The rise for the past 100 years has been 3/4 of a degree Celsius (1.3 Fahrenheit). Obviously a difference that small isn't going to keep it from snowing.
In fact, I suspect most people's reaction to this would be to wonder why in the world anyone would make a fuss about such a modest rise in temperature, given that it varies a lot more than that from day to day. So what's the big deal?
It's because we're talking about a long-term average, not short-term fluctuations about that average. There's a lot of evidence that the average had held very steady for many centuries before the current warming trend. Moreover, the rate of change is accelerating, heating up twice as fast in the last 50 years as in the previous 50. The current rate of warming may be unprecedented in thousands or even millions of years.
The climate has changed in the past (if usually not this fast), but geology and paleontology suggest that when the global average temperature has risen or fallen by a few degrees, the results have been pretty dramatic. To be more specific, a lot of research suggests that a further increase of more than a couple of degrees Celsius would lead to serious harm. In fact, we're already starting to see some of the anticipated problems. For example, biologists are reporting troubling developments attributable to warming, such as the expansion of tropical diseases and pests into more areas and shrinking habitats for cold-weather plants and animals. Several island nations in the Pacific and cities in south Florida are experiencing increased flooding as a consequence of sea-level rise.
The surface temperature is only a small part of the story. In fact, the great majority of the heat is being absorbed by the oceans. It's thermal expansion that's causing those rising sea levels. Warmer oceans also lead to more evaporation, meaning we can expect more rain and more snow in many areas where the air cools enough to precipitate out the moisture it holds. (So much for the idea that more snow means no global warming.)
This isn't just a problem for polar bears. It's a serious menace to the world's economy and the health of humans, plants, and animals, including those important to agriculture. Unless something is done soon, sea level rise and these other problems will likely force massive human migrations later in this century, leading to political disruption and war.
More directly, a higher average temperature means more heat waves. It surprised me to learn a few years ago that heat waves are the single most deadly weather phenomenon, killing far more than hurricanes, tornadoes, or floods.
I'm trying to keep this brief, so I'll just list a few earlier posts on the subject that might be of interest:
- Physicist and former global warming skeptic Richard Muller describes his research and why the data forced him to change his mind (link)
- 2014 was the warmest year on record according to multiple independent sources (link and link)
- Astronomer Phil Plait's suggested recent reading/viewing viewing on global warming (link)
- White House science advisor John Holdren corrects misconceptions from members of Congress (link)
- More misconceptions are addressed by the Veritasium science channel on YouTube (link)
- A survey of U.S. scientists finds overwhelming agreement that humans are causing climate change (link). In addition, if you look at the detailed report (link to PDF, see page 77), only 9 percent think the temperature rise is mostly from natural causes and just 3 percent doubt the Earth is warming. In addition, 94 percent consider it a serious problem, with more than 3/4 calling it "very serious."
(See also the climate change category in the right column for additional links.)
Finally, in passing, it's probably worth mentioning Al Gore didn't invent the idea of global warming any more than Margaret Mitchell made up the Civil War when she wrote Gone with the Wind. Gore just offered a book, a movie, and a series of speeches about a subject that has been widely accepted science for decades. I first learned about human-caused global warming when I was a physics major in college, and years before that it was mentioned in one of the Bell Telephone television science specials back in 1958. (I included a clip from that show at the end of this earlier post.)
(This post has been updated a couple of times for clarity.)