Carbon Dioxide and Climate: What We Knew Then, What We Know Now

We’re in the midst of a landmark period for our changing climate: the warmest year thus far in the warmest decade in global records of surface air temperature. This is also a crucial time for dialogue on climate change, as we approach a major UN meeting in Paris this December. At that meeting, delegates from around the world will try valiantly to hammer out the first entirely new global agreement in 17 years for reducing greenhouse-gas emissions. We can expect a steady drumbeat of events building up to Paris. This week, Pope Francis is expected to bring his extraordinary message on climate change to the halls of Congress in an address on Wednesday, with a massive rally for climate action scheduled for Washington, D.C., that same day. The pope then heads to New York for a Thursday address at the United Nations, where more than 150 world leaders at a summit on sustainable development are set to adopt 17 ambitious goals, one of which is “take urgent action to confront climate change and its impacts.”

Motivating all this activity is the inexorable build-up of carbon dioxide and other greenhouse gases in our global atmosphere as a result of burning fossil fuels (coal, oil, and gas). When fossil fuels are burned, carbon from the fuel joins with an oxygen molecule from the air to create CO2. Because carbon dioxide is odorless and invisible, it’s all too easy to ignore. People had a harder time ignoring the “emissions” when our land-based transportation was conducted by horse-drawn wagon!

Despite its literal invisibility, carbon dioxide is all too real a substance, and fossil fuels add a tremendous amount of it to our atmosphere. Figure 1 shows how global CO2 emissions have unfolded over the last forty-plus years (up through 2013, the most recent year with complete data). The graphic, created by WU’s Jerimiah Brown using data from the Netherlands Environmental Assessment Agency, tells us much about the situation leading to the upcoming talks in Paris.


Figure 1. Annual emissions of the greenhouse gas carbon dioxide produced by fossil fuel use and cement manufacture over the period 1970 - 2015. Cement production is only a small portion of this total, now around 5% annually. Image credit: Jerimiah Brown, Weather Underground, using data from the Netherlands Environmental Assessment Agency. Here is a high-resolution PDF version of the graphic.


A few things jump out from Figure 1:

--Global emissions are still climbing. In the year 2013, fossil fuel use and cement production put an estimated 35.3 billion metric tons of CO2 into the air (a metric ton is about 10% greater than a U.S. ton). That’s more than twice the amount emitted in 1970. Cement production is only a sliver of this total--historically about 2-3%, but now closer to 5%. Roughly 46% of the annual emissions shown in the graphic remain in the atmosphere each year, with the rest absorbed fairly promptly by oceans and land areas. As evident on the bottom half of Figure 1, emissions can drop slightly from one year to the next, as they did during the recessions of the early 1980s, early 1990s, and late 2000s. However, each recovery has led the way to still-higher global CO2 emissions. And even when the emissions do drop slightly in a given year, carbon dioxide continues to build up in the atmosphere, just as your credit-card balance goes up even when you cut back on how much you put on your card. This is why the amount of CO2 in the global atmosphere has increased every year since regular measurements began in 1958.

--Nation by nation, the United States no longer leads the pack. Back in the late 1990s, the U.S. was responsible for about 30% of global CO2 emissions, while China represented about 15%. Now the roles have switched as a result of China’s breakneck pace in manufacturing and development. In 2013, China was responsible for roughly 29% of global CO2 emissions, with the U.S. at around 15%. A substantial part of China’s CO2 emissions is the result of items being manufactured for sale in the United States and elsewhere; here’s a very helpful analysis from Carbon Brief on how this affects the global picture.

--Per capita, the U.S. is still in the driver’s seat. Because the United States has less than a quarter of China’s population, the amount of CO2 emitted per person is more than twice as much in the U.S. versus China. A few oil-producing nations in the Middle East have even higher per-capita rates, but their small populations means that they produce far less CO2 overall than the United States.

--Decades of emissions add up. When the atmosphere's stock of carbon dioxide goes up, it takes several hundred years for the oceans to absorb about 75 percent of this excess. The remaining 25 percent or so is stuck in the atmosphere for much longer--some of it for more than 100,000 years. This is why emissions from decades ago still have a big impact on climate. The list at upper left of Figure 1 shows the cumulative emissions from six top emitters, plus the 28 nations that now make up the European Union (EU28). Of the total amount of CO2 put into the air from 1970 to 2013, the US is responsible for about 22%; the EU28, about 18%; and China, about 15%. If you go back before 1970, the United States has an even larger share of the pie.

--Progress is possible. As a group, the EU28 nations are now emitting about 14% less CO2 than they were in 1990. That’s noteworthy when you consider that the EU28’s population and level of development is roughly comparable to the United States’. Back in the early 1980s, the US and EU28 had nearly identical CO2 emissions. By 2013, the US annual total was about 43% more than the EU28’s.

Commentary: what it means for the Paris talks

Whatever emerges in Paris is likely to be much different than the only global-scale agreement to date on carbon emissions: the Kyoto Protocol. Created in 1998, Kyoto was hamstrung by understandable tension between developed countries (the U.S. in particular) and developing nations (especially China and India). Many participants from around the globe felt it was unfair to restrict the right of less-prosperous countries to use fossil fuel to grow their economies after rich nations had had virtually unlimited access to it. The resulting agreement largely held back from emission restrictions for the developing world--and in response, the U.S. Congress voted 98-0 not to ratify Kyoto. The upshot is that most of the world’s economic activity since 1998 has taken place outside the bounds of the protocol, leaving the door wide open for huge global increases in CO2 emissions. Meanwhile, the European Union did even better than its Kyoto pledge, cutting its emissions of the top greenhouse gases 18% below 1990 levels by 2012.

Given the trends in Figure 1, a Kyoto-style approach clearly won’t work this time around. Any global agreement on emissions needs to include both the United States and China, as well as fast-growing India, in order to be effective. Yet it’s hard to imagine the current U.S. Congress agreeing to any globally constructed emissions cuts. Given this constraint and others, a new strategy has taken shape: each nation is coming up with its own nonbinding “pledges,” which will be enforced largely through peer pressure and perhaps eventually through economic tools such as tariffs and sanctions. An unprecedented agreement between China and the United States late in 2014 led to pledges by China to maximize its greenhouse gas emissions no later than 2030 (though this would still allow China’s total emissions to increase for more than a decade) and by the U.S. to reduce its emissions 12-19% below 1990 levels by 2025 (including emissions related to land use and forestry, which complicates the picture somewhat). Earlier this month, a group of some of the largest cities of China and the United States agreed on emission targets that in some cases are even more ambitious than the national goals.

Historic as they are, these examples above show how a patchwork of nation-by-nation agreements may end up resembling a crazy quilt. The big question facing delegates to Paris is whether such a global set of voluntary emission cuts, even if they’re adhered to, will be enough. There’s no single bright line that separates a livable climate from one riddled by disaster, but for more than 15 years, many scientists and policymakers have worked toward the commonly cited goal of no more than a 2°C global temperature rise above pre-industrial levels. In June, an analysis by the International Energy Agency showed that the combined global pledges thus far would allow a temperature rise of 2.6°C by 2100 and 3.5°C in the 2200s. Such a rise would boost the odds of irreversible physical change, such as the unstoppable melting of ice sheets. It would also raise the risk of truly serious impacts on agriculture, water and food supply, and human health, raising the specter of increased conflict and climate refugees. Some analysts are already pointing to the role of record drought in Syria as a major factor in that nation's civil war and the subsequent flood of migrants. "News reports calling the refugees the first 'climate refugees' are getting too far ahead of the curve," asserted Andrew Freedman in Mashable. "But the ongoing humanitarian disaster provides a teaching opportunity for a time not too long from now when the first true climate refugees trigger a similar situation."

New discoveries of oil, coal, and gas in recent years have led to unexpectedly abundant supplies of fossil fuel. Yet if we want to be fairly confident of avoiding the 2°C benchmark, we can only burn a small fraction of this fossil fuel--only about 20%, according to one influential estimate that was reinforced by the IPCC in 2013. Any global agreement that keeps us near the 2°C goal will indirectly force the vast majority of the world’s proven oil, coal, and gas reserves to remain in the ground. Ultimately, this would be a conservative action in the truest sense--conserving fossil fuel--but some of the world’s largest and most powerful corporations would stand to lose trillions of dollars in value if this played out. We know that at least one major firm had some sense of the dilemma more than 30 years ago. An major investigative report by Inside Climate News, now being published as a multipart series, describes how Exxon carried out extensive observational and computational research, starting as far back as the 1970s, that pointed to the huge risks posed by increasing carbon dioxide.

We now know that massive amounts of energy can be produced apart from fossil fuels, with the costs steadily dropping. A group of eminent British scientists and policy leaders has called for a Global Apollo Program--an international 10-year R&D effort to make renewable energy more affordable than fossil fuel. Such efforts will go a long way toward giving any global agreement cobbled together in Paris a fighting chance to succeed.

Dr. Ricky Rood is attending a Climate Data Summit sponsored by the Risky Business project as part of Climate Week NYC. See his WU blog post from September 19 for more about the long and very winding road to the negotiations in Paris. My post with Jeff Masters from earlier today outlines current happenings in the tropics; we'll be back with more on Wednesday.

Bob Henson