What temperature is the Earth supposed to be?
If we don't get our act together and slash greenhouse gas emissions, the UN climate change panel tells us, average global temperatures could rise by as much as 10 degrees F. by the end of the century.
But would that really be so bad? Sure, much of the South would be unbearable during the summer months (as would many of those tropical countries), but think of all that beautiful real estate in Alaska that we'd open up! And many of us here in Boston would willingly trade a dozen or more 100-degree F. days each year to wear shorts and flip-flops through October. Less snow shoveling, more Frisbee tossing. What's not to like?
Who decreed that average global surface temperatures have to stay at the 58 degrees F. or so that modern humans are used to? After all, we've experienced temperatures much higher than that in the past (by "we," I mean multicellular organisms living a half-billion years ago), and we've also had our share of ice ages. What is the "right" temperature for the planet?
Climate-change deniers love posing this question (economist Mark W. Hendrickson asked it earlier this week in a Monitor op-ed), because it makes those who try to answer it sound sentimental and unscientific. There is no "supposed to be" in nature. It is what it is.
But the question also misses the point: The alarming thing about global warming is not how high the average temperature will be, but
And it's rising really fast, compared to historical temperature shifts. The planet's surface has warmed about 1.4 degrees F. since 1880, most of it in the past 30 years. And it's accelerating. According to Britain’s Met Office, which has been recording temperature data since 1850, the next 10 hottest years after 1998 were, in order, 2005, 2003, 2002, 2004, 2006, 2007, 2001, 1997, 2008, and 1995.
When the temperature shifts this rapidly, living things may not be able to keep up. For instance, many insects, birds, and mammals time their breeding and migration based on temperature, while the many species of plants that they eat time their growth according to the sunlight. When this synchronicity gets thrown off, animals arrive on the scene before their meal is ready, the plants don't get their seeds propagated, and species start going extinct. Whether we like to admit it or not, humans are part of this ecosystem.
This has happened before. About 250 million years ago, 9 of 10 marine species and 7 out of 10 of terrestrial species suddenly went extinct in what paleontologists call "The Great Dying." They don't know exactly what caused this mass extinction, but in all major proposed scenarios – an asteroid impact, a giant volcanic eruption, and changes in the composition of ocean gases – it was the resulting shift in the earth's climate that, by throwing ecosystems out of whack, ultimately did in these creatures. Indeed, climate changes played a major role in all of the mass extinctions in the planet's history.
None of this is to suggest that global warming will wipe out humanity.