What will 2°C feel like?

Surprisingly, the most common question I get asked isn’t about whether climate change is happening. More typically, people are curious about how I feel about climate change and often ask about what worries me about the future.

Many of the scientific concepts that we use to talk about possible future climatic change are just that – complex scientific concepts. So when asked, I like to talk about how I feel about potential future climate change.

For example, climate scientists are concerned with pinning down a number for the Equilibrium Climate Sensitivity (ECS). This refers to the global average surface warming response to a doubling of atmospheric carbon dioxide concentrations after the system has settled and reached a new steady state.

In the real world, it could take hundreds of years or longer to see what temperature change would result from carbon dioxide doubling.

This concept is hard to pin down in scientific analyses and climate scientists use a combination of approaches, from both observations and climate models, to determine the ECS range.

The new IPCC report due out next week will likely report on a range of ECS values. The last IPCC report in 2007 indicated that climate sensitivity likely falls within the range of 2°C to 4°C.

Understanding climate sensitivity is undeniably important for understanding climatic process and change. But how much does the exact ECS range really matter? Does it matter to you if the temperature response in 500 years to a hypothetical doubling of carbon dioxide is precisely 3.5°C instead of 4°C?

Already there seems to be a fundamental misunderstanding in how we perceive the severity of climate impacts associated with comparatively small amounts of global warming.

Scientific consensus has settled around limiting the global average surface temperature increases to just 2°C in order to avoid “dangerous interference” with the climate system. Meanwhile, many people think that dangerous climate change won’t occur until we hit 8°C of warming or more.

Much of my recent work has focused on recent temperature extremes in Australia. Recently, we’ve had our hottest day, week, month, season and 12-month periods on record.

I regularly present my scientific results and used to have a slide I showed, depicting a Tasmanian family sheltering under a pier from a fire front. I had to remove the photo from my PowerPoint presentation because each time I turned around to talk about it, it would make me teary.

Average Australian temperatures have increased by about 0.8°C over the last century. But when the average climate is shifted by even a small amount, we can see very large changes in the frequency and severity of some extreme events.

In Australia, we’re used to dealing with a variable climate and the extremes it throws at us. The climate of our island continent is naturally variable, mostly because of the influence of El Niño-Southern Oscillation.

El Niño events are usually associated with warm and dry conditions like those that occurred during 1998 and the opposite phase La Niña events with cool and wet Australian conditions, like the very wet summer of 2011.

But unusually, this year’s record-breaking heat has occurred during the normally cool La Niña phase. Instead, our recent extremes are being dramatically influenced by greenhouse gas warming.

It is becoming increasingly unlikely that we can avoid 2°C of global warming. So what will 2°C feel like? What will happen when we have naturally warm conditions from an El Niño event occurring on top of 2°C of global warming?

Perhaps this year is a taste of the world to come. Right now, we relish unusually warm spring and winter days. But record temperatures have serious impacts.

Just outside of Sydney, tinderbox conditions occurred in early spring, following a dry, warm winter. Bushfires raged early in the season.

Further south in Victoria, we now face higher than average bushfire risk heading into the warm seasons. Wet conditions have produced high grass loads that can quickly dry out and fuel widespread fires.

Thinking of that family sheltering in the ocean from a fire front, I’m frightened of what might come in a world 1°C hotter than now.


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