After heated discussions and negotiations between nations and scientists, the United Nations Intergovernmental Panel on Climate Change (IPCC) on Monday presented options for slashing greenhouse gas emissions and extracting carbon dioxide from the air in order to avert catastrophic climate change.

Burning fossil fuels and deforestation have heated Earth's surface 1.1 degrees Celsius above mid-19th century levels, and nations have pledged under the 2015 Paris Agreement to cap global warming at "well below" 2 degrees Celsius, or 1.5 degrees Celsius (2.7 degrees Fahrenheit) if possible.

Here are some of the landmark 2,800-page report's key findings.

Peak emissions by 2025

Failing to sharply curb greenhouse gas emissions beyond national pledges before 2030 would put a 1.5 degrees Celsius world "beyond reach."

Current carbon-cutting policies would lower emissions only slightly by 2050, leading to global warming of 3.2 degrees Celsius by century's end.

Even a 2 degrees Celsius cap would become hugely challenging: Annual emissions would need to decline by 1.5 billion tons of carbon dioxide or equivalent gases (GtCO2-eq) every year from 2030 to 2050 – roughly the same annual decrease as in 2020 when COVID-19 lockdowns paralyzed the global economy.

To keep global temperatures below 1.5 degrees Celsius, 2 degrees Celsius or even 2.5 degrees Celsius, emissions must peak before 2025.

But in 2021 emissions recovered to record pre-pandemic levels of more than 40 billion tons of carbon dioxide (40 GtCO2).

At 2019 levels of emissions, Earth's "carbon budget" for a two-thirds chance of staying under the 1.5 degrees Celsius threshold will be used up within eight years.

Replace energy from fossil fuels...

If current oil, gas and coal energy infrastructure were to operate without sequestering emissions for their designed lifetime, capping global warming at 1.5C would be impossible.

Limiting the rise in global temperature to 2 degrees Celsius would mean that 30% of oil, 50% of gas, and 80% of coal reserves cannot be burned unless technology is used to catch and store the carbon dioxide released.

"The economic impact of stranded assets could amount to trillions of dollars," the report warns.

Eliminating fossil fuel subsidies could reduce emissions by up to 10% by 2030, while freeing up cash for building low-carbon public transport and other public services.

...with clean energy

By 2050, the world must transition to a "net zero" global economy in which almost all energy – not just electricity – comes from non-carbon-polluting sources to keep the Paris temperature targets in play.

Global wind capacity grew by 70% while solar photovoltaic (PV) rose by 170% from 2015 to 2019.

But solar and wind together only accounted for 8% of total electricity generation in 2019.

Taken together, low-and zero-carbon electricity generation technologies – including nuclear and hydro power – produced 37% of global electricity. The rest came from fossil fuels, especially coal.

Reduce demand for energy

So-called demand-side strategies – plant-based diets, electric vehicles, car-free mobility, telecommuting, climate-proof buildings, enhanced energy efficiencies, fewer long-haul flights – could cut carbon emissions by 40% to 70% by 2050.

"Rapid and deep changes in demand make it easier for every sector to reduce greenhouse gas emissions in the short and medium term," the report said.

Globally, households with income in the top 10% contribute up to 45% of total greenhouse gas emissions.

Curb methane

The potent greenhouse gas methane – 21 times more powerful than carbon dioxide over a 100-year time span – accounts for nearly 20% of global warming.

A third of that in 2019 was from fossil fuel production leaks. It is also generated by livestock (cows and sheep) and landfills. There are natural sources of methane as well.

To cap warming at 1.5 degrees Celsius or even 2 degrees Celsius methane emissions – which have been rising steadily – will need to drop 50% by 2050 compared to 2019 levels.

Suck carbon dioxide from the air

Even in optimistic emissions scenarios, several billion tons of carbon dioxide will need to be extracted each year from the atmosphere by 2050, and an accumulated total of hundreds of billions of tons by 2100.

"Carbon dioxide removal (CDR) is necessary to achieve net zero CO2 and greenhouse gas emissions both globally and nationally," the report says.

Strategies ranging from tree-planting to machines that chemically extract carbon dioxide from thin air will compensate for sectors of the economy that most likely won't be able to decarbonize by 2050 such as aviation, shipping and cement.

If global warming overshoots the Paris treaty targets, CDR will be also be needed to lower Earth's surface temperature.

Action is costly but...

Capping global warming at 1.5 degrees Celsius without overshooting the mark by a wide margin will require investing about $2.3 trillion a year in the electricity sector from 2023 to 2052. If 2 degrees Celsius is the target, that figure drops to $1.7 trillion.

In 2021, about $750 billion was spent on clean energy technologies and efficiency worldwide, according to the International Energy Agency (IEA).

Overall, investment in carbon dioxide reduction is deeply inadequate.

Wealthy nations are spending two to five times less than required. The shortfall is four to eight times below the $1.6 trillion to $3.2 trillion per year needed in developing and emerging countries.

Emissions reduction "pathways" likely to limit warming to 2 degrees Celsius would see a drop in global GDP of 1.3% to 2.7% in 2050, compared to a continuation of current policies. Limiting warming to 1.5 degrees Celsius would drive down GDP 2.6% to 4.2%.

...doing nothing costs more

These GDP estimates, however, do not account for economic upside of avoided climate impacts, ranging from extreme weather disasters to ecosystem collapse to reduced food supply.

"The benefits of pathways likely to limit warming to 2 (degrees Celsius) outweigh mitigation costs over the 21st century," the report concludes.

The economic benefits of reduced air pollution – which causes some 7 million premature deaths each year – would be on the "same order of magnitude" as the costs of cutting emissions, potentially even larger.

Providing universal access to modern energy services – increasing global greenhouse gas emissions by only a few percentage points – would also bring huge quality-of-life improvements.