How shaving half a degree off global warming targets could lessen the effects of climate change

Our planet is changing. So is our journalism. This story is part of a CBC News initiative entitled "Our Changing Planet" to show and explain the effects of climate change and what is being done about it.

Keeping a 1.5 C limit on global warming "within reach" is one of the key goals of the ongoing United Nations climate conference, COP26. That's the lower of two targets in the 2015 Paris Agreement on climate change. But why are there two targets? What's the difference between them in terms of impacts? Are they both reachable? Here's a closer look.

Article 2.1.a of the Paris Agreement names a key goal as: "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 above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change."

One of the key goals of COP26, which opens on Oct. 31 in Glasgow, is to "Secure global net zero by mid-century and keep 1.5 degrees within reach." 

Net zero means we are no longer adding heat-trapping greenhouse gases to the atmosphere. Some greenhouse gases might still be emitted, but they would be "cancelled out" by the removal of an equivalent amount of greenhouse gases. (This is very similar to carbon neutrality, but includes more than just CO2.)

So far, the world has warmed 1.1 C above pre-industrial temperatures, the United Nations reports.

The Conference of Parties (COP), as it's known, meets every year and is the global decision-making body set up to implement the United Nations Framework Convention on Climate Change, adopted in the early 1990s, and subsequent climate agreements.

WATCH | Inaction and inequity key concerns ahead of COP26 climate summit

UN negotiations had been looking at a target of 2 C for a long time. But in 2010, there was an agreement to review by 2015 whether the science suggested that goal needed to be strengthened. That included consideration of a 1.5 C goal, which had been called for by some groups representing developing countries. Among them was the Alliance of Small Island States (AOSIS), which represents many vulnerable countries in UN climate negotiations.  

"That process concluded that the globally agreed goal of two degrees as a kind of guardrail was not safe … for the most vulnerable," said Frances Fuller, the advisor on mitigation and science for AOSIS.

The group and its peers pushed hard during Paris negotiations, and eventually the 1.5 C target was added as one to work toward in the longer-term.

WATCH | What half a degree of warming could mean for climate change

The Intergovernmental Panel on Climate Change (IPCC) released a special report looking into the difference between 1.5 C and 2 C of warming in 2018.

Compared to 1.5 C of warming, an extra half a degree of warming would lead to more intense and frequent extremes of heat, heavy rainfall and drought, the report found.