climate change

IPCC: there are far-reaching differences between a 1.5°C and 2°C world


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By Anders Lorenzen

In Paris, in 2015 as the world’s governments agreed to the world’s first global treaty on climate change, the Paris Agreement. And, as part of that agreement, they asked the Intergovernmental Panel on Climate Change (IPCC), the UN’s climate science body,to produce, in 2018, a Special Report on global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways.

At a press conference in Incheon, the Republic of Korea on Monday IPCC was ready to unveil its report.

While the new report is still conservative, it represents the starkest warning so far from the organisation.

When the Paris Agreement was signed, policymakers agreed that warming must not exceed that of 2°C, with a door being left open to adopting the much tougher and more ambitious target of 1.5°C. Since then, the science has moved on and many scientists are adopting the view that a 2°C rise is no longer as safe as first thought. This report focuses on the difference of 1.5°C and 2°C and suggests that everything possible should be done to adopt 1.5°C as the new target as the difference is huge.

However, it does come with the caveat that limiting global warming to 1.5°C would require rapid, far-reaching and unprecedented changes to all aspects of society. But this would include clear benefits to people and natural ecosystems by limiting global warming to 1.5°C compared to 2°C and it could go hand in hand with ensuring a more sustainable and equitable society, the organisation said.

The report lists a number of climate change impacts examples which could be avoided by limiting global warming to 1.5°C compared to 2°C, or more. For instance, by 2100, the global sea level rise would be 10 cm lower with global warming of 1.5°C compared with 2°C. The likelihood of an Arctic Ocean free of sea ice in summer would be once per century with global warming of 1.5°C, compared with at least once per decade with 2°C. Coral reefs would decline by 70-90 per cent with global warming of 1.5°C, whereas virtually all (> 99 per cent) would be lost with 2°C.

The report was authored by ninety-one authors and represented review editors from forty countries, broadly reflecting the view of the climate science community. Lead Chair of the IPCC Hoesung Lee said: “With more than 6,000 scientific references cited and the dedicated contribution of thousands of expert and government reviewers worldwide, this important report testifies to the breadth and policy relevance of the IPCC.”

The authors of the report found that limiting climate change to 1.5°C would require “rapid and far-reaching” transitions in land, energy, industry, buildings, transport, and cities. Global net human-caused emissions of carbon dioxide (CO2) would need to fall by about 45 per cent from 2010 levels by 2030, reaching ‘net zero’ around 2050. This means that any remaining emissions would need to be balanced by removing CO2 from the air.

With a 1°C Temperature rise already observed globally, the report was clear in demonstrating the profound impact of climate change and the cost of inaction. Panmao Zhai, Co-Chair of IPCC Working Group I, said: “One of the key messages that come out very strongly from this report is that we are already seeing the consequences of 1°C of global warming through more extreme weather, rising sea levels and diminishing Arctic sea ice, among other changes.”  

The report emphasised that by limiting warming to just to half a degree less could have a profound impact and could give the planet crucial breathing space. That was echoed by the Co-Chair of IPCC Working Group II, Hans-Otto Pörtner, “Every extra bit of warming matters, especially since warming of 1.5°C or higher increases the risk associated with long-lasting or irreversible changes, such as the loss of some ecosystems”. He added that limiting climate change would also give people and ecosystems more room to adapt and remain below relevant risk thresholds.

The authors were adamant that the physics of achieving a 1.5°C world was entirely possible, but that inaction and the slow pace of transitioning away from fossil fuels made that job harder and more costly and would involve clear lifestyle choice changes.

Failure to do so, even if it is kept below 2 °C, would be damaging. The report states that if we were to allow the global temperature to temporarily exceed or ‘overshoot’ 1.5°C it would mean a greater reliance on techniques that remove CO2 from the air to return global temperature to below 1.5°C by 2100. The effectiveness of such techniques are unproven at large scale and some may carry significant risks for sustainable development

The report was prepared under the scientific leadership of all three IPCC working groups. Working Group I assesses the physical science basis of climate change; Working Group II addresses impacts, adaptation and vulnerability; and Working Group III deals with the mitigation of climate change.

This report, Global Warming of 1.5°C, is the first in a series of Special Reports to be produced in the IPCC’s Sixth Assessment Cycle. Next year the IPCC will release the Special Report on the Ocean and Cryosphere in a Changing Climate, and Climate Change and Land, which looks at how climate change affects land use.

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