Global warming: Deeper cuts can limit temperature rise to 1.5 deg says analysis

Limiting temperature rise to less than 1.5°C by 2100 is technically feasible, says a new analysis.

Deeper emission cuts and improvements in energy efficiency can help achieve the target, now being endorsed by more than 100 nations.

The study by researchers at the International Institute for Applied Systems Analysis (IIASA), the Potsdam Institute for Climate Impact Research (PIK), and others analyses the required climate policy actions and targets required for the task.

The 1.5 level is being supported as a safer goal than the currently agreed international aim of 2°C.

The analysis comes at a time when research bodies like Grantham Research Institute and the Centre for Climate Change Economics and Policy have warned that dangerous climate change is inevitable under the reduction commitments made so far by nations.

Global average concentration of carbon dioxide in the atmosphere has hit new records after crossing 400 parts per million this March, entering "a new danger zone".

From zero to negative carbon
The latest study published in the journal Nature Climate Change examines scenarios for energy, the economy and the environment for limiting temperature rise to 1.5°C above pre-industrial levels, and compares them to scenarios for limiting climate change to 2°C.

"Actions for returning global warming to below 1.5°C by 2100 are in many ways similar to those limiting warming to below 2°C," IIASA researcher Joeri Rogelj, one of the lead authors of the study told media.

"However, the more ambitious 1.5°C goal leaves no space to further delay global mitigation action and emission reductions need to scale up swiftly in the next decades."

More needs to be done in the new scenario in terms of additional reductions and meaningful policy action.

"In 1.5°C scenarios, the remaining carbon budget for the 21st century is reduced to almost half compared to 2°C scenarios," explained PIK researcher Gunnar Luderer, who co-led the study.

"As a consequence, deeper emissions cuts are required from all sectors, and global carbon neutrality would need to be reached 10-20 years earlier than projected for 2°C scenarios."

Not only will it require more emission reductions, but the 1.5 goal also calls for negative global carbon emissions at some time in the century.

In effect this means removal of significant amounts of CO2 from the atmosphere. This would require technological solutions like carbon capture and storage or afforestation that increases carbon sequestered in tree trunks and branches.

All the 1.5°C scenarios initially exceed the threshold somewhere in mid-century and then decline by 2100 and beyond as more carbon dioxide is actively removed from the atmosphere, says Rogeli.

Too late?
The recent IPCC Fifth Assessment Report did not describe in detail the critical needs for how to limit warming to below 1.5°C but a more recent commentary from the IPCC argued for limiting temperature rise to 1.5 deg C, saying that a two degree rise was more than what can be tolerated by marine ecosystems and marginalised human populations.

Over 100 countries worldwide, including the Alliance of Small Island States (AOSIS) and the Least-Developed Countries (LDCs), have declared their support for a 1.5°C target on climate change.

The UNEP gives a 50 to 66% chance of staying within 2C if annual worldwide emissions stabilise between 32 billion and 44 billion tonnes by 2030.

However, going by the promised national pledges on emission cuts made so far, experts at Grantham Research Institute and the Centre for Climate Change Economics and Policy at the London School of Economics are not optimistic.

The EU, the United States and China together are proposing annual emissions of between 20.9 billion and 22.3 billion tonnes by 2030, leaving about annual 23 billion tonnes for the rest of the world. But trends indicate their emissions are expected to rise to about 35 billion tonnes by 2030.

The combined total for the world then exceeds safe limits by at least 13 billion tones.

Research by various groups like the Global Carbon Project and University of California and the Scripps Institution of Oceanography has shown that the means to a two degree limit are slipping away fast.

Even a 2C warming comes with potential for damage, as it can spur five times as many hot extremes than today, and two times as many hot extremes as with a 1.5C warming.

Nations will meet in December in Paris to forge a climate deal to take over when the Kyoto pact ends in 2020.