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For the first time in human history, in May 2013 concentrations of CO2 rose above 400 ppm. 

That means in the geological blink of an eye, we’ve dumped more CO2 into the atmosphere than has built up naturally over the past 800,000 years. A foreboding fact indeed for the future of our climate, our planet and its inhabitants — plant, animal or human.

Prominent climate researchers have long warned that we must reduce the level of atmospheric carbon dioxide, or CO2, to 350 parts per million (ppm) or below in order to stabilize climate change and avoid global catastrophe. The Center for Biological Diversity, along with groups such as 350.org, is advocating strongly for this necessary standard.

Rajendra Pachauri, the United Nations’ principal climate scientist and chairman of the Intergovernmental Panel on Climate Change, has personally endorsed a 350 ppm target: “What is happening, and what is likely to happen, convinces me that the world must be really ambitious and very determined at moving toward a 350 target." And a United Nations project to quantify the financial costs of climate change on nature concluded that current climate targets just aren’t enough to save the world's coral reefs. Alex Rogers of London's Institute of Zoology declared that current levels of CO2 are already causing damage to reefs, and stabilizing atmospheric CO2 at anything above about 350 ppm will lead to further destruction.

Twenty top climate scientists issued an open letter to President Barack Obama and Congress to “call attention to the large difference between what U.S. politics now seems capable of enacting [targeting reduction to 450 ppm] and what scientists understand is necessary to prevent climatic disruption and protect the human future. . . . We and many others are of the view that these objectives are inadequate to sustain the integrity of global climate and to hold the risk of ruinous climatic change to an acceptably low level.”


While CO2 isn’t the only global warming pollutant we need to control, it’s the number-one contributor to climate change.

Before the Industrial Revolution, around 1750, atmospheric CO2 levels were hovering around 280 ppm. And in all of human history — going back more than 200,000 years — research shows that the highest CO2 concentration reached before modern times was 308 ppm. The Earth’s atmosphere for 2010 had an average concentration of 389  ppm. This high loading of atmospheric CO2 was thought to be rising by about 2 ppm per year — but in May 2013, levels at the Mauna Loa observatory in Hawaii hit 400 ppm.

Even modest increases in CO2 levels, sustained over very long periods on the geologic time scale, have meant major temperature increases and a much higher sea level — only one of many reasons these high CO2 levels are an extremely urgent cause for concern. We also know that an atmospheric concentration of 450 ppm will swiftly cause our oceans to become so acidic that critically important marine food webs will be at risk of collapse — meaning that our oceans are also desperately in need of the reduction to 350 ppm.

According to an annual report from the Global Carbon Project, the world's CO2 emissions exceeded even some of the direst predictions of climate scientists in 2007, when they increased 3 percent from 2006. Developing nations as a group took the lead in annual CO2 emissions for the first time in 2007, generating about 53 percent of the total; China is now considered by some to be the world's largest CO2 polluter, accounting for some 60 percent of the 2007 rise in worldwide emissions. Both on a cumulative and a per-capita basis, however, U.S. carbon dioxide emissions dwarf those of other countries. The report also found that the world's natural carbon sinks, oceans and forests that keep carbon out of the atmosphere, have been absorbing 3 percent less CO2 pollution since 2000 than in the first half of the 20th century.


Several lines of evidence show that allowing greenhouse gas levels to remain above 350 ppm for a sustained period of time will lead to dangerously acidic oceans, runaway global warming, and melting of the polar ice caps. Such a climate would be well outside anything experienced in the history of the human species, and would carry with it irreversible cascades of species extinctions and significant dangers for human civilization.

With current CO2 levels at 385 ppm, we’re already experiencing dramatic and frightening impacts of climate change. Recently, researchers reported that the Arctic is warmer than it's been in 2,000 years, even though it should be cooling because of changes in the Earth's orbit that cause the region to get less direct sunlight. Eric Post, an associate professor of biology at Penn State University, released a recent study on arctic warming and concluded: "The Arctic as we know it may soon be a thing of the past."

Also, paleoclimate data — the result of studying climate millions of years into the past — are leading scientists to conclude that current CO2 concentrations will give us much greater sea-level increases than models currently project. Scientists can’t yet precisely model the melting of the world’s great ice sheets in Greenland and Antarctica, but it’s clear that the ice is melting far faster than most scientists previously believed it would. Because modeling isn’t yet available for this more rapid ice-sheet disintegration, the Intergovernmental Panel on Climate Change simply left this component out of its sea-level rise projections, meaning that the approximately two feet of sea-level rise projected by the IPCC for this century under a high warming scenario is by definition a gross underestimate.


Along with Bill McKibben’s group 350.org, the Center has called for an immediate reduction of atmospheric CO2, with the goal of an overall concentration of 350 ppm or less to be achieved as quickly as possible. To accomplish that, we support the rapid phasing out of all coal-fired power plants, the highest technologically feasible vehicle-mileage standards, and a moratorium on Arctic oil and gas drilling, among other critical measures.

According to former NASA scientist James Hansen, “An initial 350 ppm CO2 target may be achievable by phasing out coal use except where CO2 is captured and adopting agricultural and forestry practices that sequester carbon.” This means no new coal plants; institution of sustainable, science-based farming and timber regimes that keep carbon locked up; and replacement of fossil-fuel technologies with low-carbon alternatives throughout the transportation, residential, industrial, and energy sectors as quickly as possible. A goal of 350 ppm will also necessitate the large-scale establishment of conservation and efficiency regulations and incentives.

Despite the preponderance of scientific evidence pointing urgently toward the need for a 350 ppm goal, even many environmental groups have not yet committed to the standard. It’s crucial that the federal government take aggressive regulatory action to reduce emissions now with a 350 ppm goal, catalyzing international action on the 350 ppm standard so that we can secure binding global agreements with the same benchmark.

Will we have the political will to get there?

There’s no doubt that 350 is an ambitious goal, but failing to get to there isn’t a viable option. To date, proposed bills in the U.S. Congress have fallen far short of the ppm goal needed to stave off global catastrophe from climate change.   At the Center, we’ve been working hard to get the 350 message out. While we advocate for new legislation and international agreements that would help us reach the 350 ppm target, we’re busy using existing environmental laws, like the Clean Air Act, to help curb global warming pollution now. The Clean Air Act has dramatically reduced air pollution over the past four decades, but is currently under attack in Congress. The Center’s Clean Air Cities campaign seeks to safeguard this critical protection and urge the Obama administration to use the Clean Air Act ambitiously and urgently. But we need your help. To learn more about the Center’s Clean Air Cities Campaign, please click here.

To find out what else you can do to help, please click here.

Photo of Cadillac Ranch © Jeanne Miller, courtesy of 350.org