SINGAPORE - Limiting damage from climate change will mean rapid and unprecedented changes to everything from energy production to transport, agriculture and buildings and all nations must play a role, the United Nations' climate panel said in a major report released on Monday (Oct 8).
The Intergovernmental Panel on Climate Change (IPCC) looked at the impacts of a rise in Earth's surface temperature of 1.5 deg C and steps that societies needed to take to limit global average temperatures to that level.
IPCC scientists and officials from 195 member nations met last week in Incheon, near the South Korean capital, to haggle over the final wording of the report and a "summary for policymakers" that clearly spells out the immense climate challenge ahead.
The conclusion is that it is possible but deep emissions cuts are needed before 2030. Any further delay and the world will overshoot 1.5 degrees and condemn economies and ecosystems to deadlier weather extremes, habitat loss, falling crop yields and ever higher sea levels.
"The message is: Over to governments. We've told you the scientific facts, the evidence. It's up to them to decide what to do with it," Dr Jim Skea, one of the report's co-chairs, told reporters from Incheon, where the report was released.
Fellow author Dr Valerie Masson-Delmotte said: "The report shows that we are at the cross-roads. And what is going to happen from now until 2030 is critical, especially for CO2 (carbon dioxide) emissions."
Economies would have to rapidly shift away from burning coal, oil and gas and invest heavily in renewable energy. It would also mean broader changes across societies, such as choice of transport, energy use, even the foods people eat.
The cost? Investments in clean energy totalling US$2.4 trillion (S$3.3 trillion) were needed every year from 2016 to 2035 and coal-fired power cut to almost nothing by 2050.
Scientists have long warned that rising temperatures will make the planet a deadlier place to live, in terms of extreme weather and loss of natural ecosystems, and generally assumed that mankind should limit warming to 2 deg C to avoid catastrophic climate change.
But the world has already warmed about 1 deg C since pre-industrial times. Even at that level, scientists say climate change is fuelling stronger storms, more extreme floods, deadlier heatwaves and wildfires, while hotter oceans are cooking coral reefs. Many of these impacts are occurring faster and harder than some scientists expected.
The IPCC study, which took nearly three years to complete and involved 91 authors from 40 nations, is the first to look in detail at the 1.5 deg C limit in terms of impacts and what it would take to keep temperatures at that level.
The 2015 Paris Climate Agreement calls for halting the rise in temperatures to "well below" 2 deg C and 1.5 deg C, if possible. Right at the end of the Paris conference, the IPCC was asked to prepare a special report on global warming of 1.5 deg C by looking at the latest science involving thousands of studies - more than 6,000 are cited.
The study was urgent because of the accelerating impacts of climate change and the relentless surge in greenhouse gas emissions. Carbon dioxide (CO2), the main greenhouse gas, reached record levels in the atmosphere last year and current pledges to cut emissions under the Paris Agreement would lead to warming of about 3 deg C.
The report is also seen as the main scientific guide for government policymakers on how to implement the Paris Agreement during the Katowice Climate Change Conference in Poland in December.
The authors say global warming is likely to reach 1.5 deg C between 2030 and 2052 if it continues to increase at the current rate, meaning the time to act is now. Based on current CO2 emissions from power stations, industry and transport, delaying deep cuts for another decade would make the 1.5 deg C target all but impossible and lock in more extreme weather, faster melting of ice caps and higher sea levels.
While the difference between 1.5 deg C and 2 deg C might seem small, some climate change impacts will be less severe by limiting global warming to 1.5 deg C.
For example, by 2100, global sea level rise would be 10cm lower with global warming of 1.5 deg C compared with 2 deg C.
The likelihood of an Arctic Ocean free of sea ice in summer would be once per century with at 1.5 deg C, compared to at least once per decade with 2 deg C, the authors say.
Coral reefs would decline by 70 per cent to 90 per cent at 1.5 deg C, whereas virtually all would be lost at 2 deg C.
"Every extra bit of warming matters, especially since warming of 1.5 deg C or higher increases the risk associated with long-lasting or irreversible changes, such as the loss of some ecosystems," said Professor Hans-Otto Pörtner, one of the report's authors.
The report finds that limiting global warming to 1.5 deg C would require "rapid and far-reaching" transitions in land, energy, industry, buildings, transport, and cities.
In the IPCC's most ambitious pathway, global net human-caused emissions of CO2 would need to fall by about 45 per cent from 2010 levels by 2030, reaching "net zero" around 2050. This means that any remaining emissions would need to be balanced by removing CO2 from the air. Replanting forests, restoring grasslands and boosting carbon stored in soils are some ways to do this.
Others could be machines that suck CO2 out of the atmosphere and bio-energy with carbon capture and storage.
Allowing the global temperature to temporarily exceed or "overshoot" 1.5 deg C would mean a greater reliance on techniques that remove CO2 from the air to return global temperature to below 1.5 deg C by 2100, it says.
But the report finds that effectiveness of some of these techniques are unproven at large scale and some might carry risks.
"This report gives policymakers and practitioners the information they need to make decisions that tackle climate change while considering local context and people's needs. The next few years are probably the most important in our history," said co-author Dr Debra Roberts.