Global warming is already dangerous

“Over the bleached bones and jumbled residues of numerous civilizations are written the pathetic words: ‘Too late.’”

Martin Luther King Jr.

I’ve been reading up on what the latest climate science says about where we are and where we’re heading, and decided the best way to present the information is in the following table. The table illustrates the warming, impacts, and feedbacks we can expect from various levels of CO2. While the politicians still talk of preventing dangerous climate change, this evidence shows that climate change is already dangerous and we are on track for unimaginable catastrophe.

The information in the table, except where otherwise hyperlinked, is taken from these resources by climate blogger David Spratt (which in turn reference scientific papers):


It should be noted much of this is cutting-edge science. We’re not talking in certainties here, but it’s all stuff that we have good reason to be concerned about, especially considering that, to date, scientists have dramatically underestimated the impacts of global warming.

Scenario Equivalent CO2 level Warming above preindustrial w/o nonlinear feedbacks (NB: these should not be considered stable states) Possible impacts, tipping points, and feedbacks (NB: we can also expect nasty surprises)
Current temperature level 335 ppm 0.75°C Around peak warmth experienced in the history of human civilization.

Many changes occurring much sooner than predicted.

Observed intensifying of heatwaves, floods, droughts, and fires; which humans are struggling to adapt to and have caused food price spikes.

Observed fall in global crop yields.

Observed biodiversity loss.

Observed halving of global coral reef area.

Observed 40% fall in phytoplankton productivity in some places.

Observed 80% Arctic sea ice loss.

Tipping point for Arctic sea ice loss, which will add 0.2-0.5°C and set off a chain reaction of tipping points.

Rate of change in Arctic is too fast for ecosystem to adapt.

Observed possible permafrost thaw.

Observed possible thaw of methane hydrates on Arctic seafloor.

Observed methane bubbling to the Arctic Ocean surface, prompting a glaciologist to say “we’re fucked”.

Observed rapid acceleration in ice sheet melt.

Tipping point for loss of some or all West Antarctic glaciers, which will add 1-5 m to sea level, displacing tens of millions, submerging island states and much Asian cropland (maybe by 2200?).

Minimum estimate of tipping point for Greenland ice sheet collapse, which will add up to 7 m to sea level.

At around this temperature level centuries ago, droughts collapsed North American civilizations.

At just above this temperature level 125,000 years ago, the poles were several degrees warmer, there was no summer sea ice in the Arctic, sea level 6-9 m higher, confirming we’re poised on strong polar feedbacks.

Current CO2 level (close to target of island states) 400 ppm 1.5°C Warmer than any climate in history of human civilization.

90% of coral reefs wiped out.

Tipping point for large-scale release of permafrost carbon, adding up to 1°C by 2100.

Best estimate of tipping point for Greenland ice sheet collapse.

Observed rate of CO2 buildup and ocean acidification 10 times faster than in mass marine extinction 55 million years ago when Earth warmed 5-9°C.

At nearly this CO2 level 3.5 million years ago (before humans evolved), global temperature up to 3°C warmer, Arctic 8-20°C warmer, no ice in northern hemisphere, sea level 20-30 m higher, maybe a permanent El Niño.

At this CO2 level 15 million years ago, global temperature 3-6°C warmer, little land ice, sea level 25-40 m higher.

Not a stable state: feedbacks would take us on toward the next scenario.

Target climate talks are supposedly aiming for, and “carbon budget” approach is based on 450 ppm 2°C Warmer than any climate experienced by human species.

Consensus on high threats of extreme weather and to ecosystems.

Coral reefs dead.

Loss of many Australian ecosystems, eg. Great Barrier Reef.

20% increase in extreme rainfall.

Glacier retreat threatens water supply for some countries.

At this CO2 level 35 million years ago, global temperature many degrees warmer, Earth was ice-free, sea level 75 m higher.

Not a stable state: feedbacks would take us on toward the next scenario.

Current greenhouse gas level (with short-lived non-CO2 gases currently masked by temporary cooling from aerosols) 480 ppm ~2.4°C Because aerosols and CO2 emissions both result from fossil fuel burning, eliminating all emissions would cause abrupt warming of 0.25-0.5°C.

Exceeds any estimate of a safe boundary.

Not a stable state: feedbacks would take us on toward the next scenario.

Outcome of current policies if they work (ie. distant targets, gas transition, carbon trading, endless talks) ~700 ppm ~4°C by 2100 Far beyond any climate experienced by human species.

Rate of temperature change unprecedented.

Incompatible with human civilization and beyond adaptation.

Ecosystem services can no longer support humanity.

Mass extinction as climate zones move too fast for species to adapt.

Ocean acidification causes food chain to collapse.

40% increase in extreme rainfall.

Southern Europe, US, most of Africa, southwest Asia, Brazil, and southern Australia turn to desert.

Northern Australia would shift to a climate non-existent on Earth today.

Hottest Australian summer (2012-13) unusually cold in new climate.

Australian heat deaths overwhelm healthcare system.

Number of extreme fire danger days in Australia doubles or quadruples.

Hotter and drier weather devastates Australian crop yields.

End of irrigated agriculture in Murray-Darling Basin.

83-100% of Amazon rainforest burns up and releases carbon.

Possible dieoff of algae, killing a carbon sink.

At least 1-2 m sea level rise by 2100.

All ice will melt over centuries, eventually raising sea level by 75 m.

Not a stable state: feedbacks would take us on toward the next scenario.

Business as usual (or outcome of current policies if they don’t work) ~1,000 ppm Up to 4°C by 2060

Up to 7°C by 2100

Up to 12°C by 2300

Half of inhabited land area too hot for humans to survive outdoors.

Economic costs = 50-99% of GDP.

Magnitude of global warming could exceed that associated with the worst mass extinction in geological history, when the atmosphere filled with explosive and poisonous gases.

At this CO2 level 50 million years ago, global temperature 16°C warmer.

The new inconvenient truth is that none of these scenarios is remotely safe. We have already gone too far. The Earth that existed before the Industrial Revolution is gone, and we are now entering an unfriendly and unstable climate that is already beginning to spiral out of our control. Human-caused global warming is the greatest threat facing humanity today.

It’s difficult to avoid the conclusion that the safest option is the one David Spratt and Philip Sutton have been proposing for years. We need not only an emergency response to cut emissions to zero as soon as possible, and eventually less than zero; we humans also must take on the hazardous role of climate engineers:

Zero emissions + drawdown CO2 + solar radiation management <335 ppm <0.75°C Would restore a safe climate by cooling the planet, reversing Arctic sea ice loss, avoiding carbon feedbacks, and preventing worst impacts of ocean acidification.

“Solar radiation management” (SRM) refers to geoengineering measures that directly cool the Earth, probably by adding aerosols (particulate air pollution) to the stratosphere to mimic the temporary dimming effect of volcanic eruptions. But SRM should not be seen as a magic bullet and certainly not as an excuse to go on polluting. Like the pollution we’ve emitted unintentionally, it will have side effects, some of them unpredictable. We’ll have to keep adding more aerosols over time because they only last a few years in the atmosphere, while much of the CO2 we emit will take centuries to be naturally absorbed even if nature continues to absorb our carbon emissions instead of adding more. And because SRM addresses temperature and not CO2, it won’t do anything to stop ocean acidification, which the above table should make clear is an ecological catastrophe in its own right.

Removing CO2 from the atmosphere will be extremely difficult, as we currently have no efficient way of doing so. It’s like trying to unscramble an egg. Our best bet is probably to try and enhance the natural carbon sinks, ala Greg Hunt. This might involve a massive program of reforestation, agricultural practices that absorb carbon, and biomass-burning power plants with carbon capture and storage. Again I must stress for the likes of Hunt, these ideas are very speculative, could prove highly expensive or impossible, are likely to have unforeseen side effects, will be impermanent because carbon moves easily between surface reservoirs, and therefore no get-out-of-jail-free card. It could take well over a century to get back below 335 ppm from the current CO2 level, let alone whatever levels we might reach if we delay action.

Like its environmental impacts, the politics of geoengineering is fraught with unanswered questions. The answers are beyond the scope of this post, but the political difficulties reinforce that geoengineering is not a grand solution, merely a stopgap to treat the symptoms it is too late to prevent.

Our inescapably urgent task is to cut global greenhouse gas emissions. As long as we continue emitting, the problem will keep getting worse. Because CO2 is already too high, we should not consider any further amount of carbon to be “burnable”. It is most important and urgent to phase out fossil fuel CO2 emissions, because they are the largest and longest-lived cause of anthropogenic global warming. We need to leave in the ground as much fossil fuel as possible, and approach zero emissions as soon as possible.

Because the effect of emissions is cumulative, it makes most sense from a climate point of view to cut global emissions steeply at first and then level off, buying us a bit more time to eliminate the rest of our emissions. It also makes sense for richer countries such as Australia to cut emissions first and fastest. That means we need to cut emissions at a rate much faster than politicians are currently talking about – on the order of 10% per year.

Climatologists Kevin Anderson and Alice Bows have argued we should start by reducing energy demand, to buy us time to scale up renewable energy to replace fossil fuels within two decades or so (which we need to do even just to avoid 2°C). More energy efficient technologies can help, but we may also need to reduce our consumption. They note that economists such as Nicholas Stern have assumed emissions reductions faster than 3%/year are incompatible with a growing economy, because historically they have only occurred during times of recession. It’s not clear whether that assumption is correct as faster cuts have never been economically modelled, and Beyond Zero Emissions argues that Australia’s energy sector at least can be decarbonized through spending only 3% of GDP per year. But if Stern’s assumption holds true, Anderson and Bows say:

the logic of such studies suggests (extremely) dangerous climate change can only be avoided if economic growth is exchanged, at least temporarily, for a period of planned austerity within Annex 1 (developed) nations and a rapid transition away from fossil-fuelled development within non-Annex 1 (developing) nations.

In my view, austerity will only be politically acceptable to the broader public if 1) the public understands and accepts the need for emergency action to combat climate change, and 2) there is a higher burden on those with highest incomes – if it disproportionately hurts the poorest and most vulnerable it will create discontent.

Climate action on an emergency scale is possible. For example, Paul Gilding has outlined a “One Degree War Plan” starting in 2018, which would halve global emissions in five years then phase them out by 2038, with net carbon drawdown for the rest of the century. What is lacking is political will.

As Anderson and Spratt like to say, there is no longer a non-radical option: it’s either radical system change and probable discomfort now, or radical economic collapse later. It is not possible to choose 2°C or any other global temperature, because such climates are very unlikely to be stable. The only choice is to continue along our course toward catastrophe, or to try and return to a near-preindustrial climate to avoid tipping points and stabilize the Earth system. The decisions made in the next few years will determine the extent of global warming for millennia. Whatever our ultimate CO2 target turns out to be, whether or not we go ahead with geoengineering, the practical implication is much the same: we must act now to decarbonize the global economy as quickly as possible.

Every time I revisit the latest climate observations, the prognosis is worse. This year alone, we’ve learned there is a scientific consensus that global warming is already impacting food security, the West Antarctic ice sheet has passed a tipping point, methane is bubbling to the Arctic Ocean surface, and to top it all the Earth has just experienced its warmest August on record.

Can we panic now?

1 comment

    • Jon on 21 September 2014 at 17:08
    • Reply

    Fascinating post James. Cheers, Jon

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