IPCC landmark report maps out five scenarios for Earth's climate future

Paris Agreement climate targets could soon be out of reach without immediate and massive greenhouse gas emission reductions, says the Intergovernmental Panel on Climate Change (IPCC) in a landmark report published Monday.

“This report is a reality check,” said IPCC Working Group I co-chair Valérie Masson-Delmotte in a statement. “We now have a much clearer picture of the past, present and future climate, which is essential for understanding where we are headed, what can be done, and how we can prepare.”

The report offers a more granular analysis of how greenhouse gases (GHGs) contribute to global temperature increases, and spells out different emission scenarios to estimate how likely it is the planet will cross the Paris Agreement goal of holding global warming to “well below 2, preferably 1.5 degrees Celsius” compared to pre-industrial levels. The IPCC estimates that from 2011 to 2020, global surface temperature was 1.09 C higher than the 1850 to1900 pre-industrial average.

The five scenarios considered range from very high emissions (doubling of global GHGs by 2050) to very low emissions (net-zero by 2050 and negative emissions thereafter), with its intermediate scenario representing emissions holding at current levels until mid-century.

“Global surface temperature will continue to increase until at least the mid-century under all emissions scenarios considered,” the report reads. “Global warming of 1.5 C and 2 C will be exceeded during the 21st century unless deep reductions in CO2 and other greenhouse gas emissions occur in the coming decades.”

The IPCC’s best estimate in its lowest-emission scenario sees warming held to 1.4 C by the end of the century, with its best estimate in the highest-emission scenario coming in at 4.4 C warming.

Tipping points ahead

As the planet warms, the IPCC warns heat waves, droughts, cyclones, and heavy rain will all become more common, posing a direct threat to agriculture and human safety. Then there is Arctic sea ice, snow cover, and permafrost that is melting and contributing to sea level rise and methane leaking into the atmosphere, potentially representing a tipping point for the Earth’s climate.

Tipping points in climate science refer to a threshold that, when crossed, lock in major damage. Scientists are still developing better understandings of how tipping points work, but they essentially represent a minefield on the road to net-zero given the uncertainty. Carbon sinks turning into carbon emitters, like Canada’s managed forest, or Greenland rapidly losing more than 18 billion tonnes of ice contributing to sea level rise are just two potential examples.

The IPCC report highlights the Atlantic Meridional Overturning Circulation (AMOC), the system of ocean currents that includes the Gulf Stream, as one important tipping point. The IPCC says the AMOC is “very likely” to weaken over the 21st century under all scenarios, but only has “medium confidence” there won’t be an “abrupt collapse” before 2100. If it collapsed, the world’s weather patterns would be dramatically impacted.

In fact, one study published last week in Nature Climate Change found evidence the AMOC was weakening, and warned a collapse would have “severe impacts” and increase the risk of cascading problems for other major Earth systems, “such as the Antarctic ice sheet, tropical monsoon systems and Amazon rainforest.”

Canada has a ‘carbon debt to the world’

“Hopefully, as our governments head to COP26, they will have all of this in mind, and they will make those new commitments as ambitious as science requires them to be,” says Pembina Institute director of federal policy Isabelle Turcotte.

“We need to do more at the federal level, (but) we also need to come back home domestically and make sure all provinces are energetically rowing in the same direction,” she said.

Canada has pledged to reduce emissions between 40 and 45 per cent below 2005 levels by 2030, but its latest modelling forecasts a 36 per cent reduction by 2030. Moreover, the IPCC previously said to hold global warming to 1.5 C there should be about a 45 per cent reduction in global GHGs from 2010 levels. Because global GHG emissions were higher in 2010 than in 2005, Canada’s commitment to lower emissions 40 to 45 per cent below 2005 levels is actually a weaker pledge than what the IPCC called for.

“We are not yet aligned with what science says the global target should be, so Canada needs to do more,” said Turcotte. “But we also need to keep in mind that Canada is a rich country that has hugely benefited from extracting and burning fossil fuels, and so we have a carbon debt to the world, and we need to do more than the global average effort.”

A recent report from the Pembina Institute found 95 per cent of Canadian emissions are not covered by a provincial or territorial 2030 climate target. It also found no jurisdiction had developed a path to net-zero. Because provinces hold jurisdiction over natural resource development, it is a major gap in the country’s climate ambition.

“Absent these provinces stepping up, Canada is unlikely to meet any climate target,” Turcotte said.

Turcotte pointed to the importance of carbon budgets as a tool for decarbonizing. One reason they are helpful is that a carbon budget lays out the amount of emissions a jurisdiction can generate. That shifts the focus somewhat away from the less important goal of net-zero by 2050 toward the more important question of how much carbon is emitted in the intervening years. She said net-zero is an “important longer-term milestone,” but the focus on it can be misleading.

“It could lead us to climate catastrophe, because net-zero is an emissions level in 2050,” she said. “What matters is the cumulative amount of CO2 we emit from now until 2050, or from now until we get to net-zero.”

John Woodside / Local Journalism Initiative / Canada's National Observer