A recent peer reviewed scientific paper (with 19 highly qualified authors) shows that even the international target of a maximum of 2⁰C average global warming above preindustrial levels could be very dangerous. The authors state that “Continued high fossil fuel emissions this century are predicted to yield:
- Cooling of the Southern Ocean, especially in the Western Hemisphere;
- Slowing of the Southern Ocean overturning circulation, warming of the ice shelves, and growing ice sheet mass loss;
- Slowdown and eventual shutdown of the Atlantic overturning circulation with cooling of the North Atlantic region;
- Increasingly powerful storms; and
- Non-linearly growing sea level rise, reaching several metres over a timescale of 50-100 years.”
The authors describe how they used climate simulations, paleoclimate data and modern observations to study the effect of the growing ice-melt from Greenland and Antarctica. Melt-water tends to stabilise ocean water columns. This induces more feedbacks which led to increases in subsurface ocean warming and ice shelf melting. The various climate feedbacks helped the authors interpret events in the latter part of the last interglacial where sea levels rose more than 6-9 metres and there were extreme storms when Earth was less than 1⁰C warmer than today.
The five predictions, and especially the cooling in the Southern Ocean and North Atlantic, differ from most existing climatic change predictions. The paper’s authors conclude that allowing average global atmospheric temperatures to rise to 2⁰C above pre-industrial levels would be dangerous.
They also conclude that global surface air temperature is not a good measure of the Earth’s “health.” This is because ice melt has a mid to long term cooling effect, which masks the overall heating trend. To stabilise Earth’s “energy balance” (a better measure) we need to stabilise greenhouse gas emissions. The level they recommend is 350ppm which is 60ppm below where we are now.
Even though this is a formal scientific paper, the authors emphasise that we have a global emergency. To address this emergency we need to rapidly phase out fossil fuel use. A better understanding of the global carbon cycle would also help us to effectively modify land use so as to reduce greenhouse gas production (e.g. from ruminants and rice production) and to most effectively take carbon out of the atmosphere. We should do this as well as rapidly phasing out fossil fuel use.
This is a profound paper that should provoke a real sense of urgency. While technological advances are improving the efficiency of machines and other equipment using fossil fuels, our increasing global population means that greenhouse gas levels in the atmosphere are still increasing. Per capita, developed nations have, and continue to, produce more greenhouse gases. We should lead efforts to rapidly phase out fossil fuel use and adopt more sustainable land use practices.
So what can we do? As I see it we firstly need to raise awareness about how urgent and serious the problem is. Secondly, we need to quickly develop coherent country and global strategies for taking the necessary actions to reduce global greenhouse gas atmospheric concentrations to 350ppm, even more ambitious than the 3 reduction scenarios analysed in Vivid Economics’ Carbon Nett Zero in NZ report to GLOBE-NZ this year.
Thirdly, we need to implement those strategies. This will include developing new tools and technology needed to make a rapid switch to a fossil-fuel free life. While doing this we need to make sure that we look after other parts of the environment (such as indigenous biodiversity and clean fresh water). There are social risks associated with not acting, acting too slowly or in a way that is seen as unfair. We should remember that warfare resulting from climate change impacts or perceived injustices in addressing the problem could in itself produce considerable amounts of greenhouse gases.
24 July 2017
 Hansen et al 2016. Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2⁰C global warming could be dangerous. Atmospheric Chemistry and Physics 16, 3761-3812.