Human activity behind nearly all warming: study

Near-surface air temperatures have increased on average around the world just over one degree Celsius since the mid-19th century.

That 1C increase has already seen more frequent and powerful extreme weather events such as droughts and floods, as well as superstorms made more deadly by rising seas.

The 2015 Paris climate accord commits nations to limit global temperature rises to "well below" 2C (3.6 Fahrenheit) and to a safer cap of 1.5C if possible. 

An international team of researchers wanted to better quantify how much warming can be directly contributed to human activity -- in the form of greenhouse gas emissions and land use change -- and how much is down to so-called "natural forcings".

These include phenomena such as large volcanic eruptions and changes in the Sun's energy output, and are often cited as drivers of warming by climate sceptics or deniers.

The researchers examined 13 different climate models to simulate expected temperature changes under three main scenarios: one in which just aerosol affected temperature, one where only natural forcings occurred, and another where greenhouse gas emissions are factored in.

Writing in Nature Climate Change, they found that human activity had contributed 0.9-1.3C to global temperatures -- exactly consistent with the 1.1C of warming observable today. 

"Our results clearly show that climate warming is primarily caused by humans," Nathan Gillet, from the Canadian Centre for Climate Modelling and Analysis, Environment and Climate Change, told AFP. 

Although the pandemic saw planet-warming emissions nosedive by about 7 percent in 2020, concentrations of carbon pollution continued to rise. 

The United Nations says it would take emissions to fall by similar levels to 2020's every year this decade in order to keep the 1.5C goal in play.