A Climate Scientist Explains Our Choices

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Climatologists have been described as the Cassandras of the modern era. We have developed the ability to see what the future may have in store for the climate, but are confronted by big industry that doesn’t want to hear it, government that mirrors big industry, and an ambivalent public.

Despite that, I’d like to set out what climate science has told us about the choices we have in the situation we’re facing.

The futures that we climatologists see diverge radically in the next few years. On one path, the world imposes rapid reductions of carbon emissions and ultimately manages to stabilise concentrations in the atmosphere at a level that would keep the warming below about 2 degrees Celsius. On the other path, we keep to our present course and bring about warming well beyond 2 degrees, perhaps 4 degrees or 6 degrees, or more.

Climatologists have picked 2 degrees as the rough number that separates "manageable" impacts from major, irreversible changes to the planet. This is not to say that the impacts would be "moderate" below 2 degrees. There would still be major impacts and a fair risk of irreversible climate changes at this level of warming. However, it is a matter of likelihoods, such that the severity of impacts and likelihood of irreversible climate changes increases rapidly thereafter. Beyond about 2 degrees we would be committing to high likelihoods of melting the Greenland and West Antarctic ice sheets. This would ultimately result in a dozen or so metres of sea level rise that will change the geography of coastal environments and cities for tens of millennia.

At higher temperature increases beyond 2 degrees the committed sea level rise would be in the vicinity of tens of metres, matching the 25 to 40-metre higher sea levels that prevailed when the earth was last 3-6 degrees warmer.

Warming beyond 2 degrees would also result in a breakdown of snowmelt-driven hydrological systems. The water resources of a significant fraction of the global population depend on the gradual release of snowmelt from large winter snowpacks in the Himalayas and other mountain regions. Loss of snowpack in these regions poses a major threat to the agricultural basis of these regions and populations.

Warming beyond 2 degrees would be accompanied by levels of carbon dioxide in the atmosphere that would lead to higher concentrations of dissolved carbon and higher acidity in the ocean. This in turn would hamper the ability of calcifying marine organisms to form shells. The consequences of this for the marine ecosystem and foodweb are largely unknown.

The release of stored methane and carbon dioxide from natural stores in the biosphere could be triggered by the warming and is more likely the greater the warming. Such feedbacks have the potential to greatly accelerate the warming and to continue that process regardless of our attempts to reduce emissions. That is, we could lose control of our ability to "regulate" the rate at which greenhouse gas emissions increase and the climate would be truly out of our control.

As I say, these are the divergent futures we have to choose from. And if we want to avoid the worst of these consequences then we face another choice: deciding how to reduce emissions in a way that makes sense.

So far humans have emitted about 520Gt (gigatons) of carbon to the atmosphere. The present rate is about 10Gt of carbon per year and is increasing at a rate of 1 to 3 per cent per year. In order to have a reasonable chance of keeping the warming of the planet below 2 degrees we can only afford to emit another 190Gt or so of carbon. At present rates we would use that allotment in less than two decades. That means that major efforts to reduce carbon emissions must commence now if we are to have any chance of staving off the warming and impacts described above. If we delay any longer we simply won’t be able to transform infrastructure, transport, and energy systems fast enough to stay within the 190Gt carbon allotment.

With a remaining "safe" allotment of carbon of only a couple of hundred gigatons, we need to pay attention to the main sources of carbon emissions: coal, oil, and land use changes. The latter can be minimised by preserving forests and practicing more sustainable agriculture. The main issue is coal, which is the largest source, and whose estimated reserves vastly exceed the 190Gt "safe" allotment.

There is no way to stay inside this allotment without a rapid phase-out of emissions from coal.

In practice, phasing out coal carbon emissions means phasing out coal. In principle, carbon capture and storage (CCS) could provide a means to burn coal without emitting all the carbon. However, CCS is expensive, and more importantly, it would come online too late to phase out coal carbon on the required timescale. CCS is not expected to be implemented at commercial scale for a couple of decades. If we wait for CCS, we guarantee that we will long exceed the 190Gt carbon allotment. CCS cannot help much in stabilising the warming at 2 degrees, and thus any strategy (such as the Australian one) that relies on CCS to continue burning coal is a strategy that accepts large, irreversible, climate change.

The remaining carbon allotment must be shared fairly if we expect to gain the cooperation of the world’s nations in reducing global emissions. Countries with the highest per capita emissions and with historical responsibility for most of the 520Gt of carbon emissions to date need to cut emissions first and fastest (to be sure, the developing world will need to cut quickly too as the remaining carbon allotment is so small). These principles are embodied in the UN climate change framework and make basic sense. Despite this, some countries in this category of high emitters have made their own actions conditional on those of poorer nations who do not bear the same historical responsibility.

In particular, the US and Australia have declared that they will not take effective action until all countries do. This stance violates the principle that the nations most responsible for the problem should act first, and it weakens prospects for meaningful cooperation in Copenhagen and beyond.

While the science of climate change is clear in pointing out the need for rapid action in order to avoid monumental climate change, the politics seem more designed to avoid responsibility than to avoid climate change. At the same time, the national media and most political parties in Australia indulge a tiny minority of so-called climate "sceptics".

While there are many uncertainties in any scientific discipline, the majority of the "sceptics’" arguments don’t particularly address them. Most of their arguments act to obfuscate the science — for example, by conflating climate variability with climate change. The notion that it has cooled since 1998 (it hasn’t: global temperatures over the past decade are the warmest in the record), and that this is evidence against greenhouse climate change (it isn’t, since the length of run is too short) is typical of this line of argument. Variations on this theme are played out across the press and blogosphere and must go some way in explaining the recent reduction in priority given by the public to climate change. When our political and media institutions continue to give a platform and apparent legitimacy to these arguments, no matter how absurd or how often refuted, it is no wonder that the public is still not resolved.

Australia has made virtually no progress in reducing carbon emissions from energy and transport to date. Most of the reductions have come about due to a reduction in the rate at which land is cleared. The Government’s preferred method for reducing future carbon emissions is an emissions trading scheme (ETS). As Richard Denniss has pointed out, that scheme is constituted in such a way that it will do very little to reduce carbon emissions in Australia for decades. Treasury modelling for the ETS shows no significant reductions from coal in Australia before 2033, when CCS is then assumed to play a role.

In the meantime, Australia proposes to allow itself to reach its emission targets by purchasing carbon offset credits from poorer countries. Australia is thus planning to make little or no contribution to the global effort to reduce carbon emissions for the next two and a half decades. The Australian trajectory for emission reductions, writ large, would quickly use up the 190Gt carbon allotment and guarantee climate changes well beyond 2 degrees.

The Australian Government’s argument is effectively that it is preferable to adapt to large climate change than to prevent it. Their argument is not usually stated in this form, but that is the inescapable consequence of their policy of postponing meaningful carbon reductions. On the one hand the Government calls for rapid action to prevent climate changes, while on the other hand it has crafted a policy that would guarantee that effective action is not taken. The Australian public is left largely unaware that the nation is opting to try to adapt to large climate change rather than prevent it occurring. One of the most fundamental issues facing this generation and those which will follow is being decided irrevocably now, largely without the knowledge that it is being decided at all.

While the Government policy of adaptation without effective mitigation is implicit, some are openly calling for an abandonment of the 2 degrees limit and preparation for adaptation to 4 degrees warming or more. I doubt that many who so calmly accept the higher limit truly understand what would have to be adapted to, or that we are effectively locking in these climate futures by our current decisions. Do they really believe that it is better to adapt to a hothouse climate with ice-free poles, massive sea level rise, dry basins, and acidic oceans than to adapt our cities and energy systems to run efficiently on alternative energy? The time to choose between these futures is upon us. If we don’t explicitly make this choice, then we choose our present course.

In that case, Australia’s policy of continuing to mine, burn, and export coal for decades will ensure that we play a pivotal role in accelerating the planet’s rapid approach to irreversible climate changes.

New Matilda

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