The climate is changing largely as a result of human greenhouse-gases entering the atmosphere, and those gases have just reached a milestone. It’s not a happy one. For the first time in at least 800,000 years (and maybe much longer), levels of heat-trapping carbon dioxide in the atmosphere are poised to top 400 parts per million (ppm) for a full day. That’s hundreds of thousands of years before modern humans evolved. Readings are taken at the Mauna Loa Observatory in Hawaii, the best representation of the world’s CO2 average. It is far enough from smokestacks and major cities that the CO2 picked up by detectors thoroughly mixed with other atmospheric gases. (See our related video on Mauna Loa Observatory and CO2 measurements).
In fact, CO2 has popped over 400 ppm for an hour at a time here and there already.
And scientists won’t declare that we’ve officially reached 400 ppm until the world goes through an entire month with average concentrations above that level – something that could end up happening by the time this month ends. By June, however, the level will drop back slightly as plants begin growing in earnest and sucking some of the CO2 back out of the air (that’s what creates the sawtooth pattern in the expanded chart below). And we won’t go completely above 400, with every month of the year at that level or above, for another couple of years.
But given the amount of CO2 we’re pumping into the air, it’s inevitable. And it’s a big deal: even if we cut back drastically on greenhouse-gas emissions in the next few years, we’ll keep adding to what’s already in the atmosphere. And once carbon dioxide enters the atmosphere. It takes a long, long time for natural process to take it out again. Most of the CO2 we’ve put up there will stay for many hundreds of years.
The early-season wildfires that flared in Southern California last week are mostly under control now — but that term “early season” may not mean much anymore. A recent Climate Central report shows that the burn season across the West is a whopping two-and-a-half months longer than it was 40 years ago. Not only that, the number of big fires has shot up over that same period – with the largest number of big fires occurring during the years with the highest temperatures. This is shown in the graphics above, (one more simplified for on-air use, the other showing more data for social media distribution).
Put it all together and you get a picture of what could be in store for the American West as climate change continues to push temperatures higher. The soil gets drier, and mountain snowpack is thinner (because more winter precipitation falls as rain). Then, what snow remains at the end of winter melts faster than it used to, so rivers run dry earlier in the summer. A recent NASA study showed that the total acreage burned in wildfires could double by 2050.
Although 2012 was one of the worst fire seasons on record, it’s not guaranteed that 2013 will be worse. Even in a world that’s warming overall, some years will be hotter than the average, while some will still be cooler — and temperature is just one factor that contributes to wildfires. But the trend is clear: the danger of wildfires is likely to increase in coming decades.
For a real-time look at the wildfires burning at any given time in the continental U.S, check out this interactive map.