{"id":22176,"date":"2012-06-05T13:49:50","date_gmt":"2012-06-05T20:49:50","guid":{"rendered":"http:\/\/blogs.kqed.org\/climatewatch\/?p=22176"},"modified":"2012-06-05T13:49:50","modified_gmt":"2012-06-05T20:49:50","slug":"400-ppm-a-milestone-that-means-everything-and-nothing","status":"publish","type":"post","link":"https:\/\/ww2.kqed.org\/climatewatch\/2012\/06\/05\/400-ppm-a-milestone-that-means-everything-and-nothing\/","title":{"rendered":"400 ppm: A Milestone that Means Everything, and Nothing"},"content":{"rendered":"

For the first time in history, the atmosphere\u2019s concentration of CO2 has topped 400 ppm<\/strong><\/p>\n

Commentary by Michael D. Lemonick<\/a><\/p>\n

\"\"
CO2 levels have been climbing since the Industrial Revolution.<\/figcaption><\/figure>\n

I\u2019m not big on taking note of milestones. They\u2019re artificial, and usually meaningless, but people get all worked up about them anyway. I don\u2019t like to stay up late on New Year\u2019s Eve, for example, because Dec. 31 is a purely arbitrary date. Nothing real actually begins the next day, but we all pretend otherwise. I have similar feelings about the first day of spring<\/a>, the temperature reaching 100\u00b0 as opposed to 99\u00b0 and all sorts of other magic-sounding dates and numbers that don\u2019t have any real significance.<\/p>\n

But since no law says I have to be consistent, I\u2019m going to take note of a milestone that happened some time in the past couple of months, and which was reported last week<\/a> by NOAA. For the first time in recorded history, and almost certainly for much longer than that, the atmosphere\u2019s concentration of carbon dioxide, or CO2, has nipped above 400 parts per million in at least one part of the world. Monitoring stations in Alaska, northern Europe, and Asia have all noted readings above that level during this past spring.<\/p>\n

In one sense, this isn\u2019t all that important. There\u2019s no meaningful difference between 399 ppm and 400, and the current world average is more like 393. Even in the Arctic, scientists know the CO2 level will drop back below 400 this summer, as trees in the Northern Hemisphere suck carbon dioxide back out of the atmosphere (you can see the annual ups and downs<\/a> as trees start growing in the spring and go into hibernation in the fall). We won\u2019t get to a world average of 400 for several years yet.
\n<\/p>\n

Climate scientists generally agree with all that, but suggest that the 400 ppm milestone is important anyway, for symbolic reasons. \u201cIt’s just a reminder to everybody that we haven’t fixed this and we’re still in trouble,\u201d Jim Butler at NOAA\u2019s Earth System Research Lab told the Associated Press.<\/p>\n

I don\u2019t know if the reminder will do much good, given the seeming indifference with which policymakers have responded to earlier CO2 milestones. I think reaching 400 parts per million anywhere in the world is crucially important for an entirely different reason: however much CO2 is in the atmosphere today is the minimum level we\u2019re going to have to live with for the indefinite future. Once carbon dioxide is swirling around in the stratosphere above us, it will stay there for hundreds and hundreds of years. It\u2019s as though you gained the most weight in your life, and knew you\u2019d never weigh even a single pound less, ever.<\/p>\n

CO2 does eventually get pulled back out of the atmosphere by natural processes, but that happens very slowly. Climate scientists like to compare the atmosphere to a bathtub half-full of water, with a very slow drain and a slowly trickling faucet. If the drain and the trickle are balanced, the water level never changes \u2014 just as the trickle of natural CO2 into the atmosphere and the drainage into trees, carbonate rocks and other places have been in balance for at least 2,000 years, and probably more. Atmospheric CO2 hovered at around 270-290 parts per million that whole time, and the climate stayed more or less stable.<\/p>\n

\"\"
Recent monthly mean CO2 measured at Mauna Loa Observatory in Hawaii.<\/figcaption><\/figure>\n

Since the wholesale burning of fossil fuels began with the Industrial Revolution, however, CO2 levels have been climbing. The faucet has been opened wider, but the drain is still very slow. And even if we manage to cut emissions significantly \u2014 something that\u2019s not looking likely anytime soon \u2014 the faucet will still open wider than it was in pre-industrial times. CO2 levels will continue to climb, just not as fast.<\/p>\n

So once we get to 400 (or 425 or 450 or 500 or whatever), that\u2019s where we\u2019ll be for the foreseeable future. The elevated temperatures caused by this crucial heat-trapping gas will be with us indefinitely as well. The world\u2019s glaciers and ice caps will continue to melt \u2014 just think of the difference between putting a small block of ice in a hot oven for 10 seconds and putting it in there for an hour. The oceans will continue to warm. As a result of both the melting and warming, sea level<\/a> will continue to rise. Scientists expect the oceans to be perhaps 3 feet higher by 2100, but it won\u2019t stop then (which means, by the way, that 2100 is another meaningless milestone).<\/p>\n

And all of that\u2019s going to be true even if we cut back drastically on emissions. If we don\u2019t, then every new CO2 milestone \u2014 500 ppm, 800, 964, whatever number you choose \u2014 will be the new the level of climate-changing pollution the planet will have to deal with at the very minimum from that time onward.<\/p>\n

Maybe that\u2019s another reason for me to ignore milestones from now on. They\u2019re either meaningless, or highly depressing. Or, as in this case, both at once.<\/p>\n

A version of this post also appears on<\/em> Climate Central<\/a>, Climate Watch’s content partner.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

For the first time in history, the atmosphere\u2019s concentration of CO2 has topped 400 ppm<\/p>\n","protected":false},"author":11421,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[6],"tags":[35,81],"coauthors":[],"series":[],"affiliates":[],"programs":[],"collections":[],"interests":[],"class_list":["post-22176","post","type-post","status-publish","format-standard","hentry","category-thescience","tag-atmosphere","tag-carbon-dioxide"],"acf":{"template_type":"standard","featured_image_type":"standard","is_audio_post":false},"yoast_head":"\n400 ppm: A Milestone that Means Everything, and Nothing | Climate Watch<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" 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