Part 1 of 4: How Warm is Too Warm?

This is the first installment of a four-part series to be published each Wednesday on Action Needed to Stop Global Warming.

1. How Warm is Too Warm?
2. Worldwide Emissions Target
3. U.S. Emissions Target
4. Technologies to Get Us There

According to the Intergovernmental Panel on Climate Change (see IPCC report [PDF] and description of the IPCC), global warming is “unequivocal”, and almost certainly due to human activities. Moreover, the IPCC says, global warming is already doing significant damage – more droughts, wildfires, heat waves, and downpours, and more intense hurricanes. What can we do about it?

We begin by considering how much warmer it can get before climate change becomes dangerous and irreversible. Unfortunately, our influence over this is limited by two factors:

• We can’t reverse the warming we have already caused. Per the IPCC report, CO₂ concentrations since the 1800’s have increased from 280 parts per million (ppm) to 380 ppm, causing global temperatures to increase by about 1.3^oF. To undo that warming, we would have to return the CO₂ concentration to its pre-industrial level. This would require removing 800,000 million metric tons of CO₂ from the atmosphere, and we just don’t have the ability to do that. To put that amount in perspective, consider that Richard Branson’s Virgin Earth Challenge will give $25 million to anyone who can remove just 0.1% of that amount.
• It’s going to get warmer than it is today. Even if we stabilized greenhouse gas concentrations today – a virtual impossibility – the rate of warming would slow, but not stop for another 30 years. This delayed warming, caused by (among other factors) how long it takes for the ocean to heat and cool, is called “warming in the pipeline”. The IPCC estimates that warming in the pipeline will increase global temperatures by an additional 1.0^oF, no matter what action we take. But we can – and better – stop it there.

Scientists have identified tipping points in the climate system for different parts of the world, beyond which major climate disruption with dangerous and irreversible impacts will occur (see our Visible Impacts report [PDF]). The most immediate of these tipping points is in Greenland, which has begun to lose its ice sheet. The ice is currently two miles thick, extends over an area equivalent to Mexico, and contains 10 percent of the earth’s fresh water.

Satellite measurements show that the Greenland ice sheet recently began losing mass and the rate of loss appears to be accelerating. Scientists estimate that if global temperatures rise 3.6^oF above pre-industrial levels (2.3 ^oF above what they are now), the melting will become unstoppable. Within 100 years or so, the Greenland ice sheet could be gone, causing a 20 foot increase in sea levels. This is not a legacy we want to leave to future generations. Imagine a world without the Everglades or Wall Street.

Since the consequences of losing the Greenland ice sheet are global and dire, the line in the sand [PDF] that scientists have drawn is the tipping point for Greenland. Global average temperatures must not rise more than 3.6^oF above pre-industrial temperatures, 2.3^oF above current temperatures, or just 1.3^oF above what the temperature will be after the warming in the pipeline takes place.

The next post in this series will discuss the emissions limits needed to keep us from crossing the 3.6^oF tipping point.