“It is unequivocal that human influence has warmed the atmosphere, ocean and land" - that is according to a new report on climate change, published this morning.

The Intergovernmental Panel on Climate Change (IPCC) has raised a "climate alarm" with the publication of Climate Change 2021: the Physical Science Basis, which warns that climate change is already affecting every region on Earth, in multiple ways.

This report, which saw hundreds of scientists review more than 1,400 studies to evaluate how human activity is contributing to the Earth's climate change, has called for immediate action to the "immediate threat" of climate change.

It found that the main human causes of climate change are the "heat-absorbing greenhouse gases (GHG) released by fossil fuel combustion, deforestation, and agriculture", among others.

Many of the changes observed in the climate are unprecedented in thousands, if not hundreds of thousands of years, the report states.

And some of the changes already set in motion - such as continued sea-level rise - are irreversible over hundreds to thousands of years, according to the IPCC.

The report shows that human activity caused the Earth's temperature to increase by 1.1°C between 1850-1900. Averaged over the next 20 years, global temperature is expected to reach, or exceed, 1.5°C of warming.

This is an average figure, with some parts of the world, for example, the Arctic, heating faster than others.

With 1.5°C global warming, there will be increasing heat waves, longer warm seasons and shorter cold seasons, according to the report.

At 2°C of global warming, heat extremes would more often reach critical tolerance thresholds for agriculture and health, the report shows.

The report also states that levels of CO2 emissions were higher in 2019 than any time in at least two million years.

And, that levels of methane and nitrous oxide - second and third-highest contributors of climate change, behind CO2 - were higher in 2019 than at any time in at least 800,000 years.

But it is not just about temperature, the report has found.

Climate change is bringing about multiple different changes in different regions, including changes to wetness and dryness, to winds, snow and ice, coastal areas and oceans.

For example:

“This report is a reality check,” said IPCC working group co-chair, Valerie Masson-Delmotte.

The report also stated that strong and sustained reductions in CO2 emissions and other GHGs would limit climate change.

While benefits for air quality would come quickly, it could, however, take 20-30 years to see global temperatures stabilise, according to the IPCC.