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The importance of that 2 degrees Celsius of warming limit

Why is climate change’s 2 degrees Celsius of warming limit so important? The Conversation, David Titley, Professor of Practice in Meteorology, Professor of International Affairs & Director Center for Solutions to Weather and Climate Risk, Pennsylvania State University, August 23, 2017

If you read or listen to almost any article about climate change, it’s likely the story refers in some way to the “2 degrees Celsius limit.” The story often mentions greatly increased risks if the climate exceeds 2°C and even “catastrophic” impacts to our world if we warm more than the target.

Recently a series of scientific papers have come out and stated that we have a 5 percent chance of limiting warming to 2°C, and only one chance in a hundred of keeping man-made global warming to 1.5°C, the aspirational goal of the 2015 Paris United Nations Framework Convention on Climate Change conference. Additionally, recent research shows that we may have already locked in 1.5°C of warming even if we magically reduced our carbon footprint to zero today………

This short history makes it clear that the goal evolved from the qualitative but reasonable desire to keep changes to the climate within certain bounds: namely, within what the world had experienced in the relatively recent geological past to avoid catastrophically disrupting both human civilization and natural ecosystems.

Climate scientists subsequently began supporting the idea of a limit of 1°C or 2°C starting over three decades ago. They showed the likely risks increase with temperatures over 1°C, and those risks grow substantially with additional warming.

And if we miss the target?

Perhaps the most powerful aspect about the 2°C threshold is not its scientific veracity, but its simplicity as an organizing principle.

The climate system is vast and has more dynamics, parameters and variations in space and time than is possible to quickly and simply convey. What the 2°C threshold lacks in nuance and depth, it more than makes up as a goal that is understandable, measurable and may still be achievable, although our actions will need to change quickly. Goals and goal-setting are very powerful instruments in effecting change.

While the 2°C threshold is a blunt instrument that has many faults, similar to attempting to judge a quarterback’s value to his team solely by his rating, its ability to rally 195 countries to sign an agreement should not be discounted

Ultimately, what should we do if we cannot make the 1.5°C or 2°C limit? The most current IPCC report shows the risks, parsed by continent, of a 2°C world, and how they are part of a continuum of risk extending from today’s climate to a 4°C.

Most of these risks are assessed by the IPCC to increase in steady fashion. That is, for most aspects of climate impacts we do not “fall off a cliff” at 2°C, although considerable damage to coral reefs and even agriculture may increase significantly around this threshold.

Like any goal, the 2°C limit should be ambitious but achievable. However, if it is not met, we should do everything we can to meet a 2¼°C or 2.5°C goal.

These goals can be compared to the speed limits for trucks we see on a mountain descent. The speed limit (say 30 mph) will allow trucks of any type to descend with a safety margin to spare. We know that coming down the hill at 70 mph likely results in a crash at the bottom.

In between those two numbers? The risk increases – and that’s where we are with climate change. If we can’t come down the hill at 30 mph, let’s try for 35 or 40 mph. Because we know that at 70 mph – or business as usual – we will have a very bad outcome, and nobody wants that. https://theconversation.com/why-is-climate-changes-2-degrees-celsius-of-warming-limit-so-important-82058

August 25, 2017 - Posted by Christina Macpherson | 2 WORLD, climate change