How Warm will Warming be?

Mark Lynas’ “Six Degrees: our future on a hotter planet” works systematically through the impact of warming the planet one degree at a time through the range of predictions for the next century. Key sentence: “none of the continent of Australia – except perhaps the extreme north and Tasmania – will be able to support significant crop production in the four-degree world because of heatwaves and declining rainfall.”

I came across Mark Lynas’ “Six Degrees: our future on a hotter planet” by way of his handy summary in the Guardian. The book itself will be published in Australia at the beginning of June. It is surprising the task hasn’t been undertaken before: what Lynas has done is to read through all of the thousands of scientific papers published over the last few years in the run-up to the IPCC 2007 publication, and provide a summary of the predicted impacts as the world warms by one degree, two degrees, up to the six degrees of the upper end of the range of predictions for this century. This is our doom: almost all climate scientists believe there is essentially no chance of our getting out of this century with less than two degrees of warming, and many think we may be lucky to get away with as little as six degrees if nothing is done (or action is delayed more than a little).

Lynas has provided a detailed summary of his work, so I will concentrate on a few specifics, and highlight some conclusions for Australia. It is interesting that much of the work is sourced from paleoclimatology rather than from climate modelling, which is to say that many conclusions are drawn from looking back rather than forward: for example, at the last interglacial (100,000 years ago) for the two-degree impacts, and the Pliocene (three million years ago) for the three-degree impacts.

Lynas notes that people can be fooled into thinking that 3 to 5 degrees of warming isn’t that bad – after all, the days in Sydney are currently ten degrees warmer than the nights (and generally a preferable temperature, at that). But variability is not the same as a higher global average, and the extremes at the higher averages will be much more extreme: for example, the four-degree rise has top summer temperatures increasing by 7 to 9  degrees in many places, bringing a Sydney New Year’s Day of 50°C into reach.

We can skip past the one and two degree steps fairly quickly since these outcomes are essentially inevitable: this is what happens even if governments everywhere start concerted action as soon as possible.

A few highlights from the inevitable are worth noting:

  • sub-tropical rain-bearing wind and weather systems will move further from the equator, meaning that drought events like those of the last few years will become more frequent and more prolonged: agricultural yields in the Murray-Darling (and Nebraska) will drop dramatically;
  • about half of Queensland’s Wet Tropics will die, along with a large proportion of the species in them; the Great Barrier Reef will bleach, bleach again, die and then dissolve as the oceans absorb carbon dioxide and become more acidic;
  • cyclones will range further south and the combination of higher sea levels and consequent storm surges will wash away many coastal areas built on sand; coal miners who have had their jobs saved by John Howard will have to holiday outside Queensland;
  • at two degrees or above, the Greenland ice shelf will melt: it may take centuries, but a 5-metre or so sea-level rise is coming sooner or later.

The Three-Degree World 

Lynas rightly concentrates the longest chapter of his book on Three Degrees. This is the stuff that can still be avoided if we do everything possible in mitigation: wind, solar, geosequestration, high carbon trading prices, lifestyle changes – the whole shooting match (with the possible exception of nuclear, which adds very little for appalling cost). More importantly, this almost certainly becomes inevitable if we waste too many years arguing about the impact on jobs or the relative economics of some of the measures. Without significant and concerted effort, we could be in the three-degree world by 2050.

Many of the key impacts here are driven by the loss of snow cover from all but the highest mountains. Snowcaps store water for the spring, and the replacement of snow with rain will make many rivers alternate between drought and flood, devastating agriculture in many of the world’s important regions. The impact may be more than climatic: for example, the loss of the upper Indus would destroy agriculture in the Punjab, leaving nuclear-armed Pakistan without adequate food, and looking across its borders at a northern India that still has irrigation capability …

Perhaps the most dangerous impact from the snow cover loss is on the Amazon. Its upper tributaries have already gone dry for a time in 2005: regular repeats risk a cycle of drying and fire that could permanently remove the Amazon rainforest from our world. The Amazon rainforest is not like Australia: major fires will leave no viable seeds and starters to regenerate, and the sheer scale of such a fire could release enough carbon to take us on to the next degree of warming.

The Three Degree chapter quotes CSIRO predictions for Australia:

  • days above 35°C in NSW could increase 2- to 7-fold by 2070, while rainfall drops by 25%
  • in northern Victoria, rainfall will drop by up to 40% 
  • the Murray-Darling basin will lose between a quarter and half its flow.

There is also the possibility of El Nino events that go on for decades or even the whole century. It’s worth quoting verbatim from the bottom of p.134 and the top of p.135:

“The combination of fire, heat and drought will make life in Australia increasingly untenable as the world warms. Farming and food production will tip into irreversible decline. Salt water will creep up the stricken river system
s, poisoning groundwater supplies. Higher temperatures mean greater evaporation, further drying out vegetation and soils, and leading to huge losses from dwindling reservoirs stored behind dams.

At the very least, these changes mean big disruptions in everyday life for the average Australian, major economic losses and strict rationing of water. At worst, they may lead to population movements out of areas with too little water, and towards Tasmania and the northern tropical region whose rainfall remains more reliable. Life may simply not be possible in much of the interior as temperatures reach scorching new highs.”

But we can all rest easy knowing that it is our PM’s considered judgment that it is better to risk all this than it is to risk losing jobs.

Four and Up 

The Four Degree world is mostly more of the same: more storms, more drought.However, another direct quote (p.186) is probably worth adding here for Australian readers:

“In addition, none of the continent of Australia – except perhaps the extreme north and Tasmania – will be able to support significant crop production in the four-degree world because of heatwaves and declining rainfall.”

I think I might just repeat the core of that, since it is a potential answer to the question “what if we do nothing because of the risk to jobs?”:

“none of the continent of Australia … will be able to support significant crop production in the four-degree world”

The most significant four-degree impact is the potential melting of tundra permafrost, and the consequent release of 500 billion tons of stored carbon as CO2 or methane: potentially making inevitable the move to the Five-Degree world, which we can illustrate by quotes from each end of Lynas’ chapter: 

“With five degrees of global warming, an entirely new planet comes into being – one largely unrecognisable from the earth we know today. The remaining ice sheets are eventually eliminated from both poles. Rainforests have already burned up and disappeared. Rising sea levels have already inundated coastal cities and are beginning to penetrate far inland into continental interiors. Humans are herded into shrinking zones of habitability by the twin crises of drought and flood. Inland areas see temperatures ten or more degrees higher than now.” (p.207)

“I find it difficult to avoid the conclusion that millions, and later billions, of people will die in such a scenario.” (p.230)

But this isn’t the worst-case scenario: there is one more degree to go before we reach the top of the range of forecasts for this century. Lynas notes that almost no climate scenarios have gone to this level, despite this being within the range of the IPCC standard scenarios. To find analogies, we have to go back to the Cretaceous, between 144 and 65 million years ago. Sea levels were 200 metres above current levels, making some homes in the Blue Mountains deep waterfront. Or, more worryingly (in case you were feeling comfortable at this point), we could go back 250 million years to the end-Permian wipeout. Deserts reached to between 45 and 60 degrees north and south, sea temperatures reached into the high 30s, killing off almost all ocean life. But human releases of carbon dioxide are happening faster than at any of these times – this is good news in terms of the time it will take for the seas to rise and warm, but not good news for any of the other species on the planet.

“Many people, when confronted by such awful possibilities, take refuge in a sort of geological fatalism: the oft-heard refrain that life will go on, with us or without us, and that at the end of the day it doesn’t really matter. …[But] it is far from clear that life will always go on.” (p.258)

What Is To Be Done?

This book describes the current best guesses of what the world will be like if it warms as predicted. The last section talks about likelihood and what can be done to change the outcome.

We had all better hope that the current scientific consensus on warming, its causes, and what can be done, is right. If the skeptics are correct, and the warming path is determined by natural forces beyond our control, then the world of four, five or six degrees may indeed be inevitable. However, since there can be no serious doubt that climate change for at least the last half-million years has been closely associated with changes in greenhouse gas concentrations, we can  hope that action is still possible.

The other main skeptical claim, that the climate models are unproven and may be unreliable is more worrying, not least because this view is increasingly being held by climate scientists themselves. But the conclusions they draw from this are very different. Since the connection between greenhouse gas concentrations and climate has been established science for hundreds of years, and is one of the keys to explaining the planet’s history for the last half-billion years, there is a missing link here, which is that greenhouse gas concentrations for the last few decades are much higher than they were in those past ages. This means that the climate may be much more sensitive to this than the models conservatively assume, and therefore the time we have left to alter the outcome is much shorter.

of this is examined in more detail in other recent books, for example Fred Pearce’s “With Speed and Violence: why scientists fear tipping points in climate change”. Lynas himself simply states his own informed view that current targets of 550ppm for CO2 and a two-degree warming are incompatible. Since the rest of his book suggests that any warming target above two degrees is indeed “dangerous climate change”, he believes that we have to try for lower greenhouse gas targets.

The current Labor and Green targets of 60% and 80% reductions by 2050 in first world countries like Australia are dangerously conservative. George Monbiot in “Heat” suggests a program for a 90% reduction by 2030 without damaging economic growth. Lynas commends this, while suggesting that this is the minimum effort we need.

The balance we have to contemplate is this: is it worth putting some Australian jobs at risk to avoid the risk of having to abandon Australia as a habitable continent by the end of the century? The Prime Minister believes that the jobs mustn’t be risked until the outcome is certain, how about you?