Why We Need to Cut Emissions as Soon as Possible

This post is by Michael Oppenheimer, Ph.D., the Albert G. Milbank Professor of Geosciences and International Affairs in the Woodrow Wilson School and the Department of Geosciences at Princeton University. He also serves as science advisor to Environmental Defense.

We’re already seeing environmental changes from global warming, and some key ones are occurring more quickly than scientists expected. Consequently, many experts from diverse disciplines are uncomfortable with the slow pace of governments in addressing this issue. The growing sense of urgency arises from two concerns:

• Earth’s climate system may be rapidly approaching a point of no return where large, irreversible and destructive changes, like the gradual disintegration of an ice sheet, become inevitable.
• To achieve any given temperature goal, the longer we delay action, the steeper emissions reductions will need to be. It’s easier to cut emissions gradually than it is to slash them drastically.

The Point of No Return

As Bill explained in his post "How Warm is Too Warm?", many experts consider one tipping point to be a warming sufficient to melt the Greenland ice sheet. Over time, this would cause sea levels to rise over 20 feet, flooding heavily populated coastal areas around the world.

In an earlier post, I showed what Florida would look like with just three feet of sea level rise (which could happen this century). Now take a look at what a 20-foot rise would do:

Source: University of Arizona’s Department of Geosciences. 6 meters equals 20 feet.

The results would be equally dramatic around the world, displacing hundreds of millions of people, flooding valuable property, and drowning wetlands that support important fisheries.

Scientists estimate that the Greenland ice sheet may begin an irreversible meltdown once global temperatures rise 2°F to 7°F above today’s level. Due to "warming in the pipeline", we may have only a little over 1°F of headroom between the current level of committed warming and the lower end of that range.

Although this outcome could play out slowly, taking more than a millennium, it also could occur rapidly, over the course of several centuries. If disintegration occurs slowly, it might be possible to stabilize the ice sheet by cooling the planet back down before the process went too far. But if disintegration is rapid, it likely would be irreversible once the threshold was exceeded.

Other major natural and social systems are at risk with only a modest warming. As the Intergovernmental Panel on Climate Change (IPCC) reported in April, grain production in some areas could begin to decline with 2°F of warming, likely leading to food shortages. A warming of 2°F would trigger increased bleaching of coral reefs, and a 4°F warming could cause widespread reef mortality. This, in turn, would harm fisheries since coral reefs provide key habitat. In fact, up to 30 percent of all species could be at risk of extinction with about 4°F of warming (see Figure SPM.2 in the Summary for Policymakers of the IPCC’s Working Group 2 report).

Climate change also threatens national security. Earlier this year, a group of high-ranking retired U.S. military leaders warned that "Climate change can act as a threat multiplier for instability in some of the most volatile regions of the world, and it presents significant national security challenges for the United States." Perhaps this view was in the minds of the committee that honored the IPCC with the Nobel Prize for Peace.

We Must Act Quickly

If we decrease emissions slowly, we can minimize the pain of shifting to a low-carbon economy. If we delay, we won’t have the luxury of gradual change.

The graph below shows global emissions from 1990 and 2100. The red line at the top represents business-as-usual. The other lines show emissions scenarios with a 50 percent chance of limiting further warming to 2°F, each one diverging from business-as-usual in a different year.

Source: Environmental Defense analysis using the MAGICC climate model.

Each of the scenarios (except business as usual) emits the same amount of greenhouse gases between now and 2100. But the longer we wait to reduce emissions, the steeper the downward slope – the faster the reduction must be. And if we wait too long, it will no longer be possible to avoid the tipping point.

Three of the opportunities on the graph are already past – it’s too late to start the transition to a low-carbon economy in 1995, 2000, or 2005. But if we start in 2010 (the solid blue line), global emissions could begin to decline before 2025. The rate of reduction starts out slowly – less than 1 percent per year – and gradually steepens until it reaches a maximum of 2.7 percent per year by 2050.

If, however, we wait until 2030 to take action, the maximum reduction rate nearly doubles to 5.2 percent per year. What does a 5.2 percent cut in emissions look like? Here are a few examples: In 2003, New York and Massachusetts accounted for 4.98 percent of all U.S. emissions. In 2000, Germany, France and the U.K. accounted for 5.28 percent of global emissions. That’s a lot of emissions to cut each year, especially with so little time to prepare.

If we act now, we have time to implement efficiency practices, scale up existing low-carbon technologies, and develop new technologies that could bring emissions down in the long term. And because we would have chipped away at emissions a for longer period, the maximum reduction rate could be much lower than if we delay.

No Excuses

One of the most common excuses people give for delay is that prompt action would be too expensive. But many studies show that the overall economic impact of early, gradual emissions reduction would be relatively modest. In fact, the looming consequences of climate change mean that doing nothing now is the most expensive choice we could make.

So there really is no good reason to delay, and every reason to act. That’s why it’s so exciting to see Congress finally talking about comprehensive legislation to stop climate change. Let’s hope they act soon.