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Emissions Reduction Pledges Fall Far Short of Copenhagen Accord Goal, UN Says

At the Copenhagen climate summit in December 2009, world leaders agreed to a non-binding yet ambitious goal: to limit global warming to less than two degrees Celsius (3.6°F) above the average global surface temperatures in the preindustrial era. To start toward this goal, they made various pledges to reduce emissions of climate-warming greenhouse gases, such as carbon dioxide (CO2).

A year later, however, against the backdrop of the next major round of international climate negotiations now going on in Cancun, Mexico, a U.N. report has found that the pledges articulated in the Copenhagen Accord are unlikely to enable the world to reach that 2°C goal.

Even if the pledges were met, says the report, released on November 23 by the United Nations Environment Program (UNEP) in conjunction with 25 research institutions and nonprofits worldwide, the amount of greenhouse gases remaining in the atmosphere would “imply a temperature increase of between 2.5 to 5°C [4.5 to 9°F] before the end of the century.”

To understand why, it’s important to understand the concept of cumulative emissions.

Carbon dioxide and certain other greenhouse gases stay in the atmosphere for a long time — in some cases, on the order of a century to millenia. This means that they can build up over years. Natural processes constantly remove CO2 from the atmosphere, depositing large amounts into the oceans and forests each year. However, because more CO2 is going into the air than nature can take out, the actual amount of CO2 in the air is rising. This trend will continue – along with increasing global temperatures — as long as emissions exceed the capacity of natural absorbers to remove CO2 from the atmosphere.

When it comes to cumulative emissions, scientists sometimes use a "bathtub analogy." If water pours into a tub faster than it can drain out, the tub overflows. The same is true for C02 in the atmosphere.

Scientists like to invoke a bathtub analogy to explain the importance — and simplicity — of cumulative emissions. Anyone who has ever taken a bath will know that even if you’ve got the drain open, the level of water in the tub will rise if water is flowing in faster than it’s draining out. 

Think of CO2 emissions (due mainly to fossil fuel burning, cement manufacture and land use) as the flow from a faucet into the world’s carbon bathtub. Biological processes on earth absorb CO2 from the air, with large amounts of the gas flowing into the oceans and forests this way each year. Think of this as the earth’s CO2 drain. Currently the earth’s faucet is putting CO2 into the tub much faster than the drain is removing it. Even if countries turn down the faucet (by meeting their pledges made under the Copenhagen Accord) the level in the tub will continue to rise as long as CO2 keeps running into the tub faster than the drain is removing it.

Because CO2 molecules emitted today will stay in the air for centuries and millennia, we need to set a cumulative limit on emissions for the foreseeable future if we want to stay below a certain temperature increase.

According to the UNEP study, we will reach this cumulative limit pretty quickly after 2020 if the world only meets its Copenhagen Accord pledges, implying that to remain within that limit our emissions after 2020 will have to be reduced very steeply. But if countries start to go beyond their Copenhagen pledges sooner, it will take longer to reach the limit, making the emissions reduction challenge after 2020 much easier.

A closer look at numbers and scenarios

The report shows that even if the most ambitious emissions reductions put on the table in Copenhagen were to be realized — a big if at this point — there would still be a sizable gap between the projected global emissions in 2020, and the emissions reductions the authors say are needed to have a high likelihood (given the range of realistic scenarios in terms of technologically feasible emission reductions after 2020) of preventing global average surface temperatures from warming by more than 2°C.

This gap would be about equal to the total emissions from all the world’s cars, buses and trucks in 2005, the study states.

As part of the Accord, 85 countries made an emissions reduction pledge — either to reduce their emissions or limit how fast their emissions would grow. However, many pledges were conditional. Some countries, for example, said they would not undertake emissions reductions unless other nations lived up to their pledges as well. Other pledges depended upon the passage of climate change legislation, which at least in the U.S., has not occurred.

The new study outlines several different future emissions scenarios, or “pathways”, based in part on whether the conditional emissions pledges are in fact implemented, and what kinds of emissions accounting rules are used, since some could result in overestimating actual emissions reductions.

The study finds that if countries continue on a “business as usual” emissions trajectory (which is to say, with no reductions at all) then global emissions could reach 56 billion tons (gigatons) of CO2 equivalent (GtCO2e) in 2020 (CO2e means actual CO2 plus the equivalent amount of CO2 it would take to generate the warming from other greenhouse gases, such as methane). By contrast, the study says global emissions will need to be about 44 GtCO2e in 2020 in order to have a reasonable shot (defined as more than a 66 percent chance) at meeting the Copenhagen Accord’s temperature goal.

These colored bands show groups of emission pathways that have approximately the same “likely” avoided temperature increase in the twenty-first century. Superimposed on top of the pathways is the range of estimated emissions resulting from the Copenhagen Accord pledges. The small black bar shows the range of median estimates from the four pledge cases. The thin blue bar represents the wider range of estimates associated with those four cases (the 20th to 80th percentile range). Credit: UNEP.

Under a “least ambitious” emissions reduction scenario (meaning that some countries use others’ failure to slash emissions as a reason not to reduce their own emissions), emissions would be cut to 53 GtCO2e, leaving a gap of 9 GtCO2e. The gap could be reduced substantially by policy options such as setting more stringent rules on how to account for land use change and forestry.

Even under the most ambitious reduction scenario, with the Copenhagen pledges fully met, global emissions would reach about 49 GtCO2e in 2020, the report states, leaving a gap of 5 GtCO2e. One way to close that remaining gap would be for individual countries to undertake greater emissions reductions on their own through domestic initiatives, the report states.

Either way, says the study, “steep emission reductions are needed” after 2020 in order to meet the 2 deg C target — how steep will depend on exactly when emissions peak, and at what level. In other words, the job will not be done even if the emissions scenario turns out to meet the goal of 44 GtCO2e. And of course, the larger the gap we still leave by 2020, the steeper and technologically more demanding the subsequent measures to make up for it will have to be.

“Keeping climate change within manageable limits is achievable, but the window of success is narrowing” with each passing year, Amy Fraenkel, Director of the UNEP Regional Office for North America, said during a conference call with reporters.