Take action now to prevent 4°C rise, says IPCC

Global warming can still be limited to 2°C in 2100, but only if action is taken now to cut energy use and decarbonise electricity, say scientists

In the third part of the Intergovernmental Panel on Climate Change’s (IPCC) fifth assessment report, scientists argue that it remains possible and cost-effective to reduce global emissions of greenhouse gases (GHGs) to levels that are likely to limit temperature rise to 2°C at the end of the century.

However, cuts must take place at a more ambitious level than those pledged by UN governments at COP16, in Cancún, and action cannot be delayed until 2030.

The report from the IPCC’s working group III, says that to keep atmospheric CO2 levels to 450-500ppm in 2100, global GHG emissions must be cut by 40%-70% by 2050 and be “near-zero” by the end of the century. Last May, the daily and weekly average levels of CO2 in the atmosphere reached more than 400ppm for the first time.

After assessing 900 mitigation scenarios, the scientists confirm that they believe the necessary reductions in GHG output are possible, but are reliant on “large-scale, global changes” to the energy sector.

The report predicts a “critical” role for bioenergy and carbon capture and storage (CCS) in abating emissions from the sector, while acknowledging that CCS is not yet a proven technology at the scale necessary.

In many of the mitigation scenarios, renewable energy technologies are expected to generate 80% of the world’s electricity in 2050. The report warns, however, that many renewables still need policy support to achieve this level of deployment.

Meanwhile, power generation from fossil fuels without CCS will need to be phased out almost entirely by 2100, with natural gas without CCS described as a “bridge technology” to replace coal-fired plants.

The report also makes it clear that emissions must be reduced from transport, industry and buildings, as well as through behavior change.

IPCC scientists predict that without further mitigation measures GHGs from industry will increase by 50%-150% on 2010 levels by 2050. However, they also estimate that the energy intensity of global industry could be cut by 25% through the wide-scale adoption of best available technologies and that a further 20% of energy savings are possible through innovations in process and product design.

The scientists highlight in particular the benefits of resource efficiency, saying that improvements in materials use, alongside greater recycling and reuse of products could help to reduce GHGs. In the long-term, new industrial processes, “radical product innovations” (such as alternatives to cement) and CCS are thought to offer “significant” GHG reductions.

The IPCC warns that a “lack of policy and experience in material and product service efficiency” remain major barriers to these GHG savings.

Another sector that will play a key role in ensuring the world can meet its carbon budget will be land use, according to the report. “Slowing deforrestation and planting forests have stopped or even reversed the increase in emissions from land-use. Through afforestation, land could be used to draw carbon dioxide from the atmosphere,” it states.

Co-chair of IPCC working group III Ottmar Edenofer said: “There is a clear message from science: To avoid dangerous interference with the climate system, we need to move away from business as usual.

“Many different pathways lead to a future within the boundaries of the 2°C goal. All of these require substantial investments. Avoiding further delays in mitigation and making use of a broad variety of technologies can limit the associated costs.”

The report estimates that the cost of mitigating climate change to 2°C will be a 0.06% reduction in annual global consumption growth, which is predicted to rise by around 1.6%-3% each year.

Commenting on the IPCC’s new report, Martin Baxter, executive director of policy at IEMA, said: “Tackling climate change is affordable, but failure to act now will reduce the chance of avoiding significant climate impacts, lock-in high-carbon infrastructure and increase long-term costs.

“We have the capability to address the challenge of climate change and make the transformation to a low-carbon, climate-resilient economy and society. We now need the political will and climate leadership to put in place a global agreement to make it happen.”

UK energy secretary, Ed Davey, reacted to the report, saying: “We need a large-scale change to our global energy system if we are to limit the effects of climate change. The longer we leave it, the more difficult and costly it will be.

“The UK is leading from the front with our European partners. We’ve adopted some of the most ambitious climate change targets and are investing in low carbon and energy efficiency technologies.”

The Mitigation of climate change report follows two other reports from IPCC working groups examining the science evidence of climate change and the predicted socioeconomic impacts of climate change. The three reports will be brought together in a final “synthesis report”, due to be published in October.