Six degrees of separation

Here is a piece I wrote that was published on 23 March 2009 in the Earth Hour special lift out of the Sydney Morning Herald and The Age.

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If the planet is like an oven, it’s still possible to turn down the temperature, writes Barry Brook.

The number is 300 and the methods will be extraordinary. In 2007, a climate awareness campaign was launched by well-known environmental author Bill McKibben. It was coined 350.org, with the slogan “350 is the most important number on the planet”.

The figure refers to a target concentration of carbon dioxide (CO₂) in the Earth’s atmosphere, in parts per million (ppm). This number was drawn from a recent study by a team of climate scientists, led by NASA’s Dr James Hansen. They showed that when long-term changes brought about by climate change are considered, the total global warming expected from a doubling of CO₂ is about six degrees.

This is clearly of great concern, because even two degrees of warming could trigger irreversible melting of the Greenland and West Antarctic ice sheets and a rise in sea levels, a large expansion of tropical zones leading to persistent droughts in the mid latitudes (including southern Australia), and longer, hotter, more frequent heatwaves and associated hazards, such as bushfires. At anywhere approaching six degrees, it’s a completely transformed planet — a world hostile to most species.

So if we expect six degrees of planetary heating with a doubling of CO₂, from 280 to 560 ppm, then the only way to avoid going over two degrees is to limit the rise of CO₂ to about 350 ppm. Hence the slogan.

An obvious problem with this goal is that we are already over 350 — and skyrocketing. Current levels stand at 385 ppm and are rising about 2 ppm each year, due to industrial emissions (burning of coal, oil and gas) and land-use changes (deforestation).

Even without further acceleration in fossil-fuel use, this would take us to 470 ppm by 2050.

Yet global energy demand is expected to double by then and progressively less CO₂ is being taken up by natural systems, as “carbon sinks” become saturated. So the hard reality is that we could be looking at 530 ppm by 2050 and a lot more in the following decades.

But there is another, more surprising, problem with 350. It’s the wrong number. While 350 ppm should give us a reasonable shot at avoiding more than two degrees of warming, that’s hardly a safe future to be aiming for. We need only to look at the impacts at less than one degree to know we’re already committed to some tough adaptation problems. These include more intense heatwaves, the rapid fall in Arctic summer sea ice, ongoing drought in Australia, sub-Saharan Africa and the western US, and the swift retreat of river-feeding mountain glaciers.

A target of 300 to 325 ppm CO₂ — the levels of the 1950s — is necessary if we wish to cut additional warming and start to roll back the already damaging impacts. As such, 350 is not a target, it’s a signpost to a goal.

So we’re aiming at 350 but the real goal is 300 and we’re already at 385. Do we give up?

No. Think of it this way, if you turned your oven up to 180 degrees, left the thermostat on that setting for a few minutes then turned it back down, how hot would it be inside the oven? Hotter than before you turned on the gas, certainly, but it wouldn’t be close to 180. Because of inertia in the internal air and surface metals, it takes time to heat the oven. If you turn back that source of energy, the temperature drops again and never reaches the thermostat reading you had set.

So, too, with climate change. It takes time to heat the oceans and to melt ice. There are lags because of the amount of energy input it takes to heat these massive systems. If you turn back the source of heat — that is, reduce the amount of greenhouse gases trapping solar energy at the Earth’s surface — then you can prevent some of the warming you might otherwise have expected.

However, the higher we turn up the thermostat (that is, the more CO₂ we release) and the longer we leave the oven on (time we take to cut emissions to zero), the closer the oven (Earth) is going to get to its final, thermostat-rated temperature (six degrees for a doubling of CO₂).

Returning to 300 is possible but the actions required will be extraordinary. An emergency mode is needed, the likes of which we have not seen since World War II.

All the zero-carbon energy cards will need to be on the table — primarily advanced nuclear power but also renewables and geothermal sources and energy efficiency. We will need ways to pull extra CO₂ out of the air through geological, chemical or biological engineering.

The response must be global and the solutions must work for all nations. Anything less and the thermostat will be set too high for too long. That’ll leave a future none of us will care to live in.

Barry Brook is Sir Hubert Wilkins chair of climate change and director of climate science at the University of Adelaide’s Environment Institute. He runs a blog at bravenewclimate.com.