Greenhouse gas emissions must be cut almost in half by 2030 to avert global environmental catastrophe, including the total loss of every coral reef, the disappearance of Arctic ice and the destruction of island communities, a landmark UN report has concluded.

Drawing on more than 6,000 scientific studies and compiled over two years, the Intergovernmental Panel on Climate Change (IPCC) findings, released this morning, warn enormous and rapid changes to the way everyone on Earth eats, travels and produces energy need to be brought in immediately.

Though the scientists behind the report said there is cause for optimism, they recognised the grim reality that nations are currently nowhere near on track to avert disaster.

The worst effects of global warming will only be prevented if the global temperature increase stays below 1.5C, a figure the scientists think will be exceeded within around 20 years.

Under current climate commitments by world leaders, the Earth will be 3C warmer by the end of the century.

“Limiting warming to 1.5C is possible within the laws of chemistry and physics, but doing so would require unprecedented changes,” said Professor Jim Skea of Imperial College London, who contributed to the report.

1.5C vs 2C: What is the difference? The new UN report focuses on the relative harm caused by two potential warming outcomes 1.5C warming will see coral reefs declining by around 80 per cent, whereas 2C would see more than 99 per cent wiped out

The Arctic Ocean will be ice-free in summer roughly once every decade under 2C warming, and only once every century under 1.5C

Melting ice will raise the sea level 10cm higher under 2C than 1.5C by 2100, a seemingly small increase that will render many islands and coastal areas uninhabitable

10 million fewer people forced from their homes by sea level rise under 1.5C warming

Roughly double the number of animals and plants will lose half their habitat under 2C warming than 1.5C

Another contributor, Professor Myles Allen from the University of Oxford, added: “If emissions rise above the current level then warming will accelerate, so we might even get to 1.5C earlier than this.”

Crucially, if the world is to avoid crossing the 1.5C threshold, CO2 emissions must be cut drastically to 45 per cent on 2010 levels by 2030, and to achieve “net zero” levels by 2050.

This means not only a massive switch away from fossil fuels to renewable energy sources, but also investing in technologies that actually suck any remaining CO2 out of the air.

The world has already passed 1C of warming since 19th-century industrialisation began spewing greenhouse gases into the atmosphere, and many regions are already suffering the effects as heatwaves, droughts and floods become more intense and frequent.

Devised by the IPCC, the aim of the new report was to establish what the world can expect in two distinct global warming futures: 1.5C and 2C.

Climate scientists used to think that 2C was a suitable level at which to cap global warming, but when the Paris climate agreement was settled in 2015 it reflected a changing consensus.

10 photographs to show to anyone who doesn't believe in climate change Show all 10 1 /10 10 photographs to show to anyone who doesn't believe in climate change 10 photographs to show to anyone who doesn't believe in climate change A group of emperor penguins face a crack in the sea ice, near McMurdo Station, Antarctica Kira Morris 10 photographs to show to anyone who doesn't believe in climate change Floods destroyed eight bridges and ruined crops such as wheat, maize and peas in the Karimabad valley in northern Pakistan, a mountainous region with many glaciers. In many parts of the world, glaciers have been in retreat, creating dangerously large lakes that can cause devastating flooding when the banks break. Climate change can also increase rainfall in some areas, while bringing drought to others. Hira Ali 10 photographs to show to anyone who doesn't believe in climate change Smoke – filled with the carbon that is driving climate change – drifts across a field in Colombia. Sandra Rondon 10 photographs to show to anyone who doesn't believe in climate change Amid a flood in Islampur, Jamalpur, Bangladesh, a woman on a raft searches for somewhere dry to take shelter. Bangladesh is one of the most vulnerable places in the world to sea level rise, which is expected to make tens of millions of people homeless by 2050. Probal Rashid 10 photographs to show to anyone who doesn't believe in climate change Sindh province in Pakistan has experienced a grim mix of two consequences of climate change. “Because of climate change either we have floods or not enough water to irrigate our crop and feed our animals,” says the photographer. “Picture clearly indicates that the extreme drought makes wide cracks in clay. Crops are very difficult to grow.” Rizwan Dharejo 10 photographs to show to anyone who doesn't believe in climate change Hanna Petursdottir examines a cave inside the Svinafellsjokull glacier in Iceland, which she said had been growing rapidly. Since 2000, the size of glaciers on Iceland has reduced by 12 per cent. Tom Schifanella 10 photographs to show to anyone who doesn't believe in climate change A river once flowed along the depression in the dry earth of this part of Bangladesh, but it has disappeared amid rising temperatures. Abrar Hossain 10 photographs to show to anyone who doesn't believe in climate change A shepherd moves his herd as he looks for green pasture near the village of Sirohi in Rajasthan, northern India. The region has been badly affected by heatwaves and drought, making local people nervous about further predicted increases in temperature. Riddhima Singh Bhati 10 photographs to show to anyone who doesn't believe in climate change A factory in China is shrouded by a haze of air pollution. The World Health Organisation has warned such pollution, much of which is from the fossil fuels that cause climate change, is a “public health emergency”. Leung Ka Wa 10 photographs to show to anyone who doesn't believe in climate change Water levels in reservoirs, like this one in Gers, France, have been getting perilously low in areas across the world affected by drought, forcing authorities to introduce water restrictions. Mahtuf Ikhsan

Its first goal was to keep global temperature rise “well below” 2C, but added that nations would “pursue efforts to limit the temperature increase even further to 1.5C”.

Many countries, particularly those consisting of low-lying islands such as the Marshall Islands, saw any warming beyond this lower bound as an effective death sentence – predicting their homes would be engulfed by rising sea levels.

After the summit the UN asked the IPCC to establish what the real-world difference between these two targets would be, and what would be needed to achieve them.

Following a week of scientists and government delegates hashing out its final wording in the South Korean city of Incheon, the conclusions of the Special Report on Global Warming of 1.5C were revealed to the world on Monday.

Though the harm caused by 1.5C warming is not trivial, the results showed stark differences between the two targets.

Unlike 2C, the lower target will see corals decline by about 80 per cent, an ice-free Arctic summer every century and 10cm less sea level rise. This seemingly small difference in sea level rise will have a massive impact for coastal regions and islands, preventing 10 million people from losing their homes to the waves.

Crucially, if the world is to avoid crossing the 1.5C threshold, carbon emissions must be cut drastically to achieve “net zero” levels by 2050. This means not only a massive switch away from fossil fuels to renewable energy sources, but also investing in technologies that suck any remaining CO2 out of the air.

Aiming for 1.5C in the UK The IPCC report has massive ramifications for every country that is serious about tackling climate change One of its key recommendations is that the world must arrive at “net zero” carbon emissions by 2050, meaning any CO2 entering the atmosphere must be sucked back out. The UK has already joined a 19-strong global Carbon Neutrality Coalition, which is pushing to deliver net zero emissions, and clean growth minister Claire Perry has said following the IPCC report she will ask government advisers to investigate the potential for the UK to tighten its climate targets. Labour has expressed its support for building a net zero emission economy by 2050. For UK citizens, the report will mean a big shake-up with a rapid switch to renewable energy and electric cars, changes to home insulation and massive tree-planting efforts. While Britain has made great strides in its switch to renewable energy, campaigners have criticised some aspects of UK energy policy as incompatible with the IPCC’s recommendations – particularly its continued support for fracking.

Carbon capture techniques may allow the world to “overshoot” the 1.5C mark before bringing it back below the threshold, but this could be a risky strategy.

While some of these measures are straightforward and proven to work – namely “nature-based” methods like planting trees – others are untested technologies that some experts fear will not meet expectations.

Whatever leaders decide to do, the scientists warned that changes will need to happen fast, and they will certainly impact people’s lives.

Shifts towards less resource-intensive diets such as those that include less meat, and the rollout of electric cars to replace high-polluting petrol and diesel models are among the changes that will help with this transition in the coming decades.

“There is not one thing you can do like going vegan that will solve everything; it will have to be a little bit of everything,” said Dr Heleen de Coninck of Radboud University.

“There is, however, no reason to assume we cannot lead a comfortable and fulfilling life in a 1.5C world.”

Dr Debra Roberts, who also contributed to the report, said in creating it they had given those in power the tools to make these important decisions. Their results will be put to the test at the next major climate change meeting this December in Poland.

“The next few years are probably the most important in our history,” said Dr Roberts.

As key nations like the US and Australia appear to turn their backs on global climate agreements, the scientists also noted that efforts to stop warming would go hand in hand with eradicating global poverty and making the world a fairer place.

The report was welcomed by experts across the scientific, business and NGO communities, who noted that the urgency of the IPCC scientists must now be mirrored by politicians.

“We have the targets, we have the solutions and the difference between impossible and possible is political leadership,” said Dr Stephen Cornelius, chief advisor on climate change at WWF

Professor Mark Maslin, a climatologist at University College London, said the report was nothing short of “revolutionary”.