At COP21 in Paris we committed to a temperature target of well below 2 degrees C and aspire to limit global warming to 1.5C, and to decarbonize after 2050. We need to examine pathways to 1.5C to see if it is possible. Dr Joeri Rogelj is one of the few researchers who has studied 1.5C pathways.
This seminar was put on by the Australian-German Climate Energy College at Melbourne University.
So what will it take to achieve 1.5C? Is it possible?
From the seminar advertising:
"With the Paris Agreement, the world decided to pursue best efforts to limit warming to below 1.5C, partly because climate impacts around 2C are considered too risky and too high by many. This seminar will put a spotlight on the mitigation side, i.e. how much and how quickly would emissions need to be reduced to still have a chance of keeping or returning warming to below 1.5C relative to pre-industrial levels.
"How does a roadmap towards a 1.5C future differ from one for 2C? How big is the task of negative emission technologies, such as biomass and CCS.
"In this seminar Joeri Rogelj will present the latest scientific literature on 1.5C emission scenarios, abatement costs, mitigation technologies, and carbon budgets.
"After Joeri Rogelj's presentation, Erwin Jackson, Deputy Director of the Climate Institute, will provide a debate contribution in regard to the Paris decision on 1.5C and Australian and international climate policy.
Melbourne author of 'Climate Code Red' and activist David Spratt (see Climate Code Red blog) made this summary, emailed to me, based upon Rogelj's May 2015 paper - Energy system transformations for limiting end-of-century warming to below 1.5 °C (abstract), his seminar talk, plus questions and conversation at the end.
- The 1.5C scenario is a 50% scenario, that is 50% of not exceeding 1.5C and 50% of exceeding it.
- This scenario has a rough 33% chance of exceeding 2C and ~10% chance of exceeding 3C.
- ALL 1.5C scenarios involve "overshoot" of target and then cooling back to target by 2100 using drawdown.
- The overshoot is up to 1.7C (see diagram, left, vertical blue dashed line)
- The carbon budget for 1.5C scenario is 200–415 GtCO2 from 2011 to 2100.
- Given we are doing around 40 GtCO2 per year at the moment, the budget from 2016 is ~0-200 GtCO2
- In other words, as of now there is no carbon budget left for 1.5C for even a 50% chance of exceeding the target by 2100
- In other words, from now on for 1.5C we have to draw down every ton of carbon we emit.
- The 1.5C scenario with overshoot requires net zero emission by 2045-2060. If emissions follow on or near the Paris path to 2030, the 1.5C scenario is not feasible.
- The 1.5C with overshoot requires large drawdown mainly using BECCS. By ~2050 this is 15GtCO2e or approx 4GtC. BECCS yields around 1tC/per year/hectare, so this implies biomass from around 4 billion hectares of land. By way of comparison, the total land applied to cropping globally is presently around 3 billion hectare. This is a huge issue, let alone whether sequestration is safe and economic.
As Rogelj says, models are very conservative, don't assume breakthroughs. But they are also optimistic in how fast society can change. I would also add that society, when motivated, can also change quite rapidly. As Erwin Jackson from the Climate Institute said in the seminar, #1o5C target brings people into the heart of discussion about how we more rapidly decarbonise. Paris changed the momentum.
We need to make the impossible possible for the millions of people who even at 1.5C will suffer innundation including many island nations, and people living in Delta areas: the Sundarbans in India, Bangladesh; Mekong River delta in Vietnam, Nile delta in Egypt to name a few.
Professor Myles Allen, a professor of geosystem science at the Environmental Change Institute, School of Geography and the Environment and Department of Physics, University of Oxford, and Director of the Oxford Martin Net Zero Carbon Investment Initiative, argues at Carbonbrief that stabilising temperatures at 1.5C, while far from guaranteed, is clearly not out of the question.
A study in May 2015 found that 1.5 degrees target is still achieveable, but only just.
Here are a few graphics I collected in December 2015 on the differences between 1.5C and 2C pathway impacts:
This chart shows clearly that between 1C and 1.5C of global warming damage to coral reefs rises quickly, but some are still likely to survive. However by 2 degrees C of warming destruction of coral reefs will approach 100 per cent. A few resilient individual species and some deepwater corals may survive, but shallow reef ecosystems will have collapsed and transitioned to a much less diverse biodiversity based on algae and seaweeds.
Comparing the likely impacts at 1.5C and 2C temperatures. For sea level rise the difference might be much greater than that stated in this graphic. A new study by Deconto and Pollard (2016) postulated that dynamic collapse of Antarctica through two newly modelled processes - hydrofracking and ice-wall collapse - may contribute up to 1 metre to sea level rise just from Antarctica.
Watch the video:
Read how the seminar unfolded on twitter: