The IPCC Gets Real about the 1.5°C Target

, director of science & policy | October 8, 2018, 12:00 pm EST
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This post is a part of a series on IPCC2018

The Special Report on Global Warming of 1.5°C  released today by the Intergovernmental Panel on Climate Change (IPCC), provides a stark profile of the disruptive climate futures we face with rising temperatures and the ‘rapid and far-reaching’ transitions across major sectors of the global economy that are now needed if warming is to be limited to 1.5 degrees Celsius above pre-industrial levels.

As a climate scientist and former IPCC lead author, this is by far the most sobering and urgent IPCC report I have read.

Why this report, now?

In the 2015 Paris Agreement, 195 nations set the goal of holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C.

They made initial, modest, “nationally determined contributions” to reduce emissions of heat-trapping gases that, if achieved, would limit global temperature increase to about 3°C by the end of this century.

They established formal mechanisms to take stock of the level of ambition pursued and that needed to meet the Agreement’s temperature goals.

And they called on the IPCC to report on “the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways” in advance of their first review of the adequacy of countries’ collective actions this December at the UN climate conference in Katowice, Poland.

The impacts of warming at 1°5 versus 2°C

Extreme weather events across the globe have been intensifying after just 1°C increase in the global average temperature. The Special Report finds that limiting further global temperature increase to 1.5°C rather than 2°C, would:

  • Limit the further increase in the number of extremely hot days across most regions, with lower risks for heat-related morbidity and mortality;
  • Limit the extent of increased flooding from extreme precipitation, including  rainfall associated with hurricanes;
  • Lower the rate of sea level rise, exposing an estimated 10 million fewer people to associated risks by 2100;
  • Limit the reduction in yields and nutritional quality of rice, wheat and other major crops;
  • Pose far lower risks of species extinction and impacts on terrestrial and wetland ecosystems and the services they provide to humanity;
  • Substantially reduce risks to marine biodiversity, ecosystems and their services, especially in Arctic sea ice and warm water coral reef ecosystems – avoiding the virtually complete loss of warm water coral reefs that is projected to result from 2°C warming; and
  • Prevent the thawing of some 2 million square kilometers of permafrost over centuries.

It is important to bear in mind that that the IPCC wasn’t charged with looking at devastating impacts associated with the ~3°C world we are now hurtling toward.  The 2°C “upper bound” of this report is far below the path we are on today. Time is of the essence to bring about the rapid and far reaching transitions that we need to protect our communities and the natural world upon which we all depend from massively disruptive climate change.

The fierce urgency of now

Keeping global temperatures from rising above 1.5°C is an essential and daunting task.

It would require, most critically, bringing global emissions of carbon dioxide to ‘net-zero’ by mid-century. That is, on average, no more carbon dioxide could be released to the atmosphere than is withdrawn.

We are far from that goal today.

The burning of coal, oil and natural gas and the clearing of forests together release more than forty billion metric tons of carbon dioxide now released each year, driving a steady increase in carbon dioxide concentrations in the atmosphere.

All pathways to limit the global temperature increase to 1.5° C would require “rapid and far-reaching transitions in energy, land, urban and infrastructure (including transport and buildings) and industrial systems.” Such transitions would be “unprecedented in scale” and require “deep emissions reductions in all sectors, a wide portfolio of mitigation options and a significant upscaling of investments in those options.”

For the energy sector, modeled pathways considered by the IPCC rely heavily on a massive transition to renewable energy, some nuclear energy and fossil fuels with carbon capture and storage, and a virtually complete phase-out of coal.

The 1.5°C pathways considered by the IPCC also assume that we will have a robust portfolio of technologies and approaches available by mid-century to draw carbon dioxide out of the atmosphere at scale. From planting trees to capturing and storing the carbon dioxide produced when biomass is burned for electricity, to technologies that might one day directly capture and store carbon dioxide from air, these carbon dioxide removal (CDR) technologies today vary widely in their “maturity, potentials, costs, risks co-benefits and trade-offs”.

Rather than banking on any one approach, the IPCC suggests that the “feasibility of CDR could be enhanced by a portfolio of options deployed at smaller scales, rather than a single option at a large scale.”

Perhaps the most sobering conclusion I take-away from this report is that the 1.5°C target, however daunting the challenge it is to limit temperatures to this level, is hardly the floor we should be seeking to stand indefinitely upon. Throughout the Special Report, the IPCC reminds us of how severe and, potentially, catastrophic, even temperature rise at this apparently modest level may be.

In considering long-term sea-level rise, for example, the Special Report finds that “instabilities…triggered by 1.5°C to 2°C of warming” could drive “irreversible loss of the Greenland ice sheet” leading to “multi-metre sea level rise over hundreds to thousands of years”.

Translation:  If we care about Earth’s future on a time scale of our grandchildren’s grandchildren, we should be looking into ways to keep global temperature rise even lower than the lower bound of the Paris temperature targets.

I believe that this requires us to take a serious look at the potential and profound risks of  “solar radiation management” technologies to reflect sunlight to cool the Earth, as a supplement to driving carbon emissions to net-zero;  technologies that this Special Report rightly notes may be “theoretically effective” but face “large uncertainties and knowledge gaps and risks, institutional and social constraints to deployment.”

Climate change is bringing upon us a world of hurt and hard choices. And, as all major challenges do, it also brings us a world of opportunity for leadership, innovation, risk-taking and the potential for transformational change.

It is time to step it up.

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