‘1.5C to stay alive’: Is the Paris Agreement’s most optimistic climate target still within reach?

Five years on from the signing of the historic climate deal in Paris, Daisy Dunne asks a range of scientists how likely it is that the agreement’s most ambitious aim can still be met

Very Severe Cyclonic Storm Nivar hit India and Sri Lanka in November 2020 (AFP via Getty Images)

One point five to stay alive. That’s the famous slogan that was first adopted by a group representing small island developing states in the Caribbean and later taken up by young climate activists, NGOs and politicians from across the world.

It’s a message that conveys, for some, that limiting global temperature rise to 1.5C above pre-industrial levels by the end of the century, the most optimistic target of the Paris Agreement, is seen as the only acceptable outcome for our planet. This is a view often held by those in developing world countries, who have done the least to cause the climate crisis yet stand to lose the most from its impacts.

Writing in The Independent , the prominent Ugandan climate activist Vanessa Nakate says: “I was driven to act by what I was witnessing around me: people in my country losing their homes, their incomes and their lives to extreme weather ... I can tell you, a 2C hotter world is a death sentence for countries like mine.”

Five years ago this week, almost all of the world’s countries pledged to limit global warming to “well below” 2C above pre-industrial levels and to strive to keep temperatures at 1.5C by the end of the century as part of the historic Paris Climate Agreement.

A landmark report published in 2018 laid out how different the world might look at 1.5C of global warming versus 2C, the upper limit on global temperatures agreed upon by countries under the Paris deal.

The report, put together by the Intergovernmental Panel on Climate Change (IPCC), a leading independent group of climate scientists, found that limiting warming to 1.5C rather than 2C could spare more than 10 million people from the impacts of sea level rise, greatly stem further increases to heat extremes and stop tropical coral reefs from disappearing completely.

However, today, global average temperatures are already around 1.2C above pre-industrial levels. And current policies from world leaders would put us on a path to around 3C of warming by the end of the century.

“We’ve long had this very glaring disconnect between the targets of the Paris Agreement and the commitments that countries have made,” Dr Zeke Hausfather, a climate scientist and director of climate and energy at the Breakthrough Institute, an environmental think tank in California, told The Independent.

Analysis by Dr Hausfather for the climate website Carbon Brief last week found that, according to projections from the latest models, the world might first exceed 1.5C between 2026 and 2042 if little is done to tackle emissions, and between 2026 and 2057 if stringent actions are taken to meet the goals of the Paris Agreement.

“If we had to give a best estimate for when the latest models think we will pass 1.5C, it’s probably around 2032,” he said.

However, very recent moves from leaders of major economies across the world allow some room for optimism, he added.

In the summer of 2019, the then UK prime minister Theresa May pledged that the country would reach net zero emissions by 2050. This was followed by similar pledges from the EU, Japan and South Korea this year.

China, the world’s largest emitter, shocked the world in October when it too announced intentions to reach “carbon neutrality” – at a slightly later date of 2060. And in November, president-elect Joe Biden vowed to commit the US, the world’s second emitter, to net-zero emissions by 2050 when he enters the White House.

A recent rapid analysis by Climate Action Tracker (CAT), an independent research group, found that if all of these new net zero pledges are met by 2050, it could hold global average temperatures in 2100 to as low as 2.1C above pre-industrial levels.

Prof Niklas Höhne, a climate scientist and founding partner of the NewClimate Institute in Germany who conducted the analysis for CAT, told The Independent: “Climate Action Tracker has looked at the temperature impact of what countries are doing for 10 years now. 

“Usually, it is a bit frustrating because not much has changed in the past, we were basically always getting in the direction of 3C of warming by the end of the century. Now we’ve seen that significantly change for the first time and that is because more and more countries are taking the idea of reaching net zero seriously.”

However, it is worth noting that this new 2.1C result relies on countries rapidly turning their net-zero pledges into action, he added.

“The second step, and even more difficult one, is to enact short-term policies to put the countries on track to meet their long-term goals,” he said. “And there we must unfortunately say that no single country has policies in place to put them on a pathway to a net-zero goal.”

In recent days, both the UK and the EU have made new short-term pledges to increase the speed at which they will slash emissions by 2030. However, the policies needed to achieve these more ambitious targets have not yet surfaced.

“These short-term pledges are absolutely essential,” Dr Joeri Rogelj, director of research and lecturer in climate change and the Environment at the Grantham Institute at Imperial College London, told The Independent.

“First of all, you don’t drop emissions down from today’s level in a single year, you need a long-term path. Having deep, early reductions lowers the maximum amount of warming that we have to contend with.”

Climate Action Tracker’s analysis came up with a central estimate of 2.1C, but it is worth bearing in mind there is still uncertainty surrounding this figure, said Prof Höhne.

“When we put out these temperature estimates we said 2.1C, but the full range for the estimate is 1.7 to 2.7C. That is something we should not forget. It could be much worse, but it could also be better.”

The range in estimates is linked to uncertainty about how the climate system will react to much higher levels of greenhouse gas emissions in the atmosphere.

Climate scientists have spent years trying to understand how “sensitive” the Earth’s climate could be to much higher CO2 levels. To do this, researchers have been trying to figure out how much the world will warm in response to a doubling of CO2 levels in the atmosphere, when compared to pre-industrial times. This estimate is known as the “climate sensitivity”.

Research suggests that the climate sensitivity lies somewhere between 1.5C and 4.5C.

If it is at the lower end, temperature rise by the end of century might be lower than 2.1C, said Prof Höhne. If it is at the higher end, warming could be more severe.

However, either end of the range would not see current net-zero pledges hold temperatures at 1.5C. For this to occur, more countries would need to commit to reaching net-zero emissions, said Prof Höhne.

He said: “So 127 countries now have net-zero goals and they cover two thirds of greenhouse gas emissions. But it means that a third are still missing.

“That other third would need to come in and reduce their emissions in the same way. But I think now that we have critical mass, I’m not as worried about this other third anymore because they will have to come onboard if they want to make trade with other countries.”

The real challenge for 1.5C remains getting all countries to increase their ambition in the short term, he added.

Cutting emissions at the pace needed to hit net zero by 2050 will not be an easy task for any country, said Dr Hausfather: “We’re not just talking about building a lot of wind and solar, we are talking about decarbonising every single sector of the economy: agriculture, industry, transport, aviation.”

The IPCC’s landmark 1.5C report examined the possible pathways the world could take to limit global warming to 1.5C by the end of the century. Though some pathways foresee the world getting to 1.5C through emissions cuts alone, many suggest that the use of “negative emissions technologies” – techniques to remove CO2 from the atmosphere – may be needed to soak up some of our pollution.

The range of negative emissions technologies currently available vary in their level of development, scalability and potential side effects.

A lot of 1.5C scenarios include the use of a technology called bioenergy with carbon capture and storage (BECCS). Put simply, this technology would involve growing crops to absorb CO2 from the atmosphere, burning these crops to produce bioenergy and then capturing the resulting emissions from the air to store in land or under the sea.

BECCS has been piloted but has not yet been developed at a large scale. Using BECCS alone to keep global warming to 1.5C would require the use of vast amounts of land for the bioenergy crops to be grown, which would compete with space needed for wildlife and food production.

“We’re really talking about potentially planetary-scale engineering here to really meet that target,” said Dr Hausfather.

Other commonly proposed negative emissions techniques, such as tree planting, would also take up space. And some, such as “direct air capture” – the idea of using machines to suck CO2 directly from air – are still far from being a commercial reality.

However, if a range of different negative emissions techniques were deployed alongside stringent emissions cuts, it could give us a fair shot at limiting global warming, said Dr Rogelj.

“While the IPCC special report on land highlighted these important risks and trade-offs [for negative emissions], it also shows if you implement best practices, these trade-offs can be avoided.”

However, even if efforts to cut emissions are ramped up and negative emissions technologies are developed at scale, it would still not guarantee that global warming is kept to 1.5C, he added.

“I think for 1.5C, we have to be lucky in some ways. Even if we follow that very steep pathway towards mid-century, that gives us a 50 per cent that we end up at 1.5C. We do exactly what we have to do and we still might end up with higher warming.”

However, it is important to understand that 1.5C and 2C are societal targets, rather than key trigger points in the Earth system, he added. That means that, while crossing the 1.5C limit is not desirable, it will not lead to sudden runaway climate change – and every action taken to limit global warming will still matter.

“At the end of the day, climate is more of a matter of degrees rather than thresholds,” added Dr Hausfather. “It would be great to limit global warming at 1.5C, but if we end up at 1.6 or 1.7C, the world doesn’t end.

“It is a useful target to have to guide the ambition of countries but at the same time it is somewhat a political construct.”