evidence: The last ice age peaked around 21,000 years ago. This was followed by 10,000 years of warming that brought us to the climate we know now, says David McGee, an associate professor in the MIT Department of Earth, Atmospheric and Planetary Sciences. During that time, global temperatures rose by about 6° Celsius (around 11° Fahrenheit). The amount of carbon dioxide (CO2) in the atmosphere—the main planet-warming greenhouse gas responsible for today’s climate change—rose too, by nearly 50%. [...] "At the end of the last ice age, ecosystems had a good deal of time to adapt to the warming as it occurred," he says. "Right now, they have much less time because warming is happening a lot faster." Past periods of warming certainly caused instability, says McGee. "The end of the last ice age wasn't a smooth ride. Sure, it was slow and natural: it occurred over 10,000 years, which is a long time. Even so, that 10,000 years was punctuated by really dramatic shifts." But the current pace of climate change is likely to be even more disruptive.