LONDON: From record-breaking temperatures to devastating storms and floods, 2023's extreme weather has highlighted the urgency of tackling climate change.

"Humanity has opened the gates of hell," U.N. Secretary-General Antonio Guterres told a Climate Ambition Summit in New York.

He said climate action is "dwarfed by the scale of the challenge" but the tide can be turned if governments and businesses "turn up the tempo".

An extensive U.N. assessment on climate progress, called the Global Stocktake, warned this month that more effort was needed "on all fronts" to curb warming and avoid its worst impacts.

So what have countries already done to deal with global warming - and how should they step things up?

What are the world's countries doing about climate change?

The U.N. Paris Agreement adopted in 2015 gave countries a goal: to limit global average temperature rise to "well below" 2 degrees Celsius (3.6 Fahrenheit) above pre-industrial times while "pursuing efforts" for a tougher ceiling of 1.5C (2.7F).

Since then, there has been "near-universal" action towards these targets, with government policies to cut planet-heating emissions across various sectors, said the U.N. stocktake.

Renewable energy such as wind and solar has rapidly developed, for example, and is expected to become the largest source of global electricity generation by 2025, according to the International Energy Agency (IEA).

But a landmark series of global scientific reports have said countries must increase the ambition of their plans and carry them out more quickly, especially to phase out the extraction and use of fossil fuels - coal, oil and natural gas.

Despite the urgency, countries are missing U.N. deadlines to submit updated climate plans under the Paris Agreement more than half the time, according to the London-based International Institute for Environment and Development (IIED).

Has there been progress on climate?

In short, yes. Future temperature rises are expected to be less extreme, thanks to government commitments to reduce greenhouse gas emissions.

In 2010, global temperature increases were projected to be between 3.7 and 4.8C in 2100, compared to pre-industrial times, but that range has been brought down to between 2.4 and 2.6C in 2022, according to the U.N. Intergovernmental Panel on Climate Change (IPCC).

This, however, is still well above the 1.5C target that scientists say is a crucial point when impacts like heatwaves, droughts and flooding become ever more frequent and severe.

The IPCC says meeting the 1.5C goal would require cutting greenhouse gas emissions by 43% by 2030 from 2019 levels.

But energy-related emissions of carbon dioxide, the main man-made greenhouse gas, rose to a record high in 2022, according to the IEA.

To get climate action on track will require a dramatic acceleration, from halting deforestation to transforming the ways humans travel, work and eat - such as reducing high-polluting plane journeys and meat consumption.

Is extreme weather normal now?

Scientists are becoming increasingly adept at connecting the dots between extreme individual events and climate change.

Record heat in Europe and North America in July 2023, for example, would have been "virtually impossible" without the impacts of climate change, according to World Weather Attribution, an international group of scientists.

The same group said Libya's heavy rainfall in September, which triggered deadly floods, was up to 50 times more likely due to human-caused warming.

As extreme weather becomes more frequent and widespread, funding to help developing countries protect their people and assets needs to increase by up to 10 times, according to the United Nations - through measures like strengthening infrastructure or restoring nature as a flood buffer.

Will we ever solve the climate crisis?

The window of opportunity is narrowing to cut greenhouse gas emissions fast enough to slow the planet's warming and stay within the 1.5C limit, scientists and U.N. officials say.

Breaching it could lead to a range of dangerous "tipping points" - or points of no return - such as the collapse of ice sheets in Greenland or Antarctica which could turbo-charge sea level rise, or the mass death of tropical coral reefs in warming oceans.

But there are positive tipping points, too.

Electric vehicle sales could soon surge as prices fall to near parity with fossil-fuel vehicles, for example.

Given the right protection, forests, peatlands and other ecosystems can thrive - capturing and absorbing human-caused emissions.

Solutions to the climate crisis already exist, but they require unprecedented changes at a new scale and pace across societies, says the IPCC.

And even if global warming does exceed 1.5C in the coming years, it adds, every fraction of a degree matters to limit the harm to people and the planet - and to help pull temperatures back down to safer levels when the time comes.