IPCC Special Report On Global Warming of 1.5°C

A detailed look at the main points of the IPCC's landmark special report on limiting global temperature rise to 1.5 degrees Celsius, published in October 2018.
IPCC Special Report 1.5 Global Warming Summary

The Special Report on Global Warming of 1.5 Degrees Celsius (SR15) was produced in October 2018 by the Intergovernmental Panel on Climate Change (IPCC) at the request of the signatories to the Paris Agreement. 1 The report’s key message is that achieving a 1.5°C (2.7°F) target is possible but exceptionally difficult, since it will require dramatic changes in all aspects of society.

The report’s climate models show that a 45 percent reduction in greenhouse gas emissions will be needed by 2030, levelling off at “net-zero” emissions by 2050. 1

Limiting global warming to 1.5°C will not avoid ecological disaster (90 percent of all tropical coral reefs will die-off) but it may avoid the far more serious consequences of a 2°C rise (99 percent of corals will die-off). 2

To understand something of the difference between 1.5°C and 2°C , see our article: Why does a Half-Degree Rise in Temperature Make Such a Difference to the Planet?

NOTE: “Global warming of 1.5°C” means an increase of 1.5°C (2.7°F) over “pre-industrial levels”. The term “pre-industrial levels” has become associated with the average temperature of the period 1850-1900, because global temperature measurements were first introduced in 1850. For more, see our article: When Did Global Warming Start?

Special Report on Global Warming of 1.5°C: Headline Conclusions

The IPCC’s Special Report on Global Warming contains three headline conclusions:

• Meeting a 1.5°C (2.7°F) target is both affordable and feasible even though it lies at the most ambitious end of the Paris pledge to limit temperature increases to 2°C above pre-industrial levels. For example, it would require “deep emissions reductions” and “rapid, far-reaching and unprecedented changes in all aspects of society.”

The report maps out two pathways to keep warming to 1.5C, using differing combinations of land use and technological change – with investment in climate technology being a critical factor. Reforestation is essential in both pathways as are shifts to electric transport systems and greater use of carbon capture and storage technology.

• Keeping the temperature rise to 1.5°C rather than 2°C would lessen the impacts on earth’s biosphere, while a 2°C temperature increase would exacerbate extreme weather events, rising sea levels, ocean deoxygenation, coral bleaching and the melting rate of Arctic sea ice, along with many other adverse effects.

• Computerized climate modelling shows that, in order to limit global warming to 1.5°C, major progress on creating a sustainable energy system is essential. “Global net human-caused emissions of carbon dioxide (CO2) would need to fall by about 45 percent from 2010 levels by 2030, reaching net zero around 2050.” 1

The report was commissioned by the UNFCCC during the Paris Climate Agreement (2015), in an attempt to fashion a sharper global response to the growing climate crisis and get governments moving. And so the IPCC – the lead scientific adviser to all UN climate talks – was invited to draft a Special Report on global warming of 1.5°C, which could explain the effects of the likely global temperature projections.

The Special Report on Global Warming (SR15) was compiled by 91 lead authors from 40 countries of residence, assisted by 133 contributing authors. It features more than 6,000 cited references as well as 42,001 expert comments.

SR15 is the first of three Special Reports to be released during the IPCC’s Sixth Assessment Cycle. The others include “The Ocean and Cryosphere in a Changing Climate“, and “Climate Change and Land“, which investigates the relationship between climate change and land use.

Special Report on Global Warming of 1.5°C: Key Points

Here is a short summary of the key points of the report. 3

Paris Agreement Won’t Stop Global Warming

Even if all signatories to the Paris Climate Agreement fulfil their Nationally Determined Contributions (NDCs), net greenhouse gas emissions will increase compared to 2010. And if warming continues at current rates, global mean temperatures are likely to rise to 1.5°C above pre-industrial levels between 2030 and 2052. Thereafter, the Earth is likely to heat up by 3-4°C by 2100. 1

Limiting Temperature Increase To 1.5°C Needs Drastic Action

Stabilizing global warming at 1.5°C is technically feasible within the laws of physics, says the report. But global emissions of carbon dioxide would have to fall by about 45 percent (from 2010 levels), by 2030, and to ‘net zero’ by 2050. Even to limit it to 2°C, would require CO2 emissions to fall by 25 percent by 2030, and to ‘net zero’ by 2075. 4

Non-CO2 emissions should also fall: for example, methane (CH4) and nitrous oxide (N2O) should be cut by 35 percent, by 2050. 1 The report says that such dramatic reductions in greenhouse gas emissions will entail dramatic changes in energy consumption and in the use of fossil fuels, like coal, its precursor peat, as well as petroleum and natural gas.

To achieve 1.5°C, the report warns that the following changes would be needed:

• By 2050, renewable energy to supply half to two-thirds of primary energy. Only about 8 percent of global electricity will be generated by natural gas, and no more than 2 percent by coal. Any use of fossil fuels will be offset by carbon capture and storage techniques. Sources of renewable energy will supply about 70–85 percent of electricity, while the use of nuclear energy is also projected to increase. 1 See: Is Nuclear Energy a Replacement for Fossil Fuels?

• The report states that these targets can be met through a combination of new and existing technologies, involving electric vehicles, the use of hydrogen, sustainable bio-based feedstocks, product substitution and carbon capture and storage (CCS). No doubt smart technology and artificial intelligence will also play their part.

• Another essential element in all 1.5°C projections, is the large-scale deployment of carbon dioxide removal measures (also called negative emissions), in the order of 100–1000 gigatonnes (GtCO2) of CO2 over the 21st century. These measures include afforestation and/or reforestation such as tree planting, soil carbon sequestration, direct air carbon capture and storage. Nearly all these will have beneficial impacts on water, land, biomass and bioenergy, if deployed on a large scale, as well as agricultural and food systems, biodiversity and other ecosystem functions. The necessity for carbon dioxide removal can only be avoided if global emissions decline by the late 2020s.

• Many scientists now believe that only stringent, across-the-board carbon taxes will galvanize governments and corporations into adopting the sort of climate action policies that are needed to cope with the crisis. For more on this and other climate action plans with ethical implications, see: The Ethics of Climate Change.

Big Difference Between 1.5°C And 2°C

The report demonstrates that the half-degree difference between a temperature rise of 2°C or 1.5°C can lead to far different outcomes for several elements in the Earth’s ecosphere.


Sea level rise is one of the most serious effects of global warming. Global sea levels rose about 20 centimeters (8 inches) in the last century. The rate of increase over the last 20 years, however, is nearly double that of the last century and the rate is accelerating every year. Water levels will continue to rise well beyond 2100, when it is projected to be up to 77cm (2 feet 6 inches) higher than the 1986–2005 baseline (assuming a 1.5°C increase), or about 87cm (2 feet 10 inches) (assuming 2°C).

Exceeding 1.5°C means placing tens of millions of people at risk of impacts like saltwater damage, flooding and the inundation of Pacific islands, as well as destabilizing the already weakened Greenland and Antarctic ice sheets. Ice melt remains a dangerous tipping point that – once exceeded – could lead to an irreversible multi-meter rise in sea level, with catastrophic results. 1 Meantime, with Arctic sea ice disappearing at a rapid rate, scientists are forecasting an Arctic Ocean free of sea ice in summer once in every 100 years at 1.5°C, compared with once every 10 years at 2°C.

Which Cities Will No Longer Be Habitable If Sea Levels Rise?

If sea levels rise three feet, low-lying U.S. cities such as New Orleans, Miami, Houston, New York, Atlantic City, Charleston and Virginia Beach would experienced regular flooding. Storm surges would lead to the submergence of large areas. In Europe, coastal areas of the Netherlands would flood, along with parts of London. Certain Pacific Island states, including Tuvalu, Kiribati, Solomon Islands, the Maldives and the Marshall Islands, would likely become uninhabitable. In Asia, a rise of only 50 cm (20 inches) would impact seriously on the cities of Jakarta, Manila, Dhaka and Shanghai, while a sea level rise of 1 meter (3.3 feet), would inundate the coastal areas of Bangladesh, uprooting many of its 35 million inhabitants.


Limiting global warming to 1.5°C is likely to restrain the worst effects of global warming on oceans, such as marine heatwaves and coral bleaching, and benefit ocean oxygen levels, and so reduce risks to marine biodiversity, fisheries, and ecosystems. For example, a 1.5°C rise in temperature will destroy 70-90 percent of all coral reefs, whereas 99 percent are projected to disappear with 2°C. 1


Loss of biodiversity and the extinction of species will be lower at 1.5°C although thousands of species will be affected. Of 105,000 species studied, 6 percent of insects, 8 percent of plants and 4 percent of vertebrates are predicted to lose over half of their “climatically determined geographic range” if global warming reaches 1.5°C, compared with 18 percent of insects, 16 percent of plants and 8 percent of vertebrates, at 2°C. 1


Roughly 4 percent or 13 percent of the Earth’s land area is projected to undergo a transformation of ecosystems at 1°C or 2°C, respectively. Northern tundra and boreal forest biomes are especially at risk of climate change-induced degradation and loss. 1 The Amazon Rainforest biome is expected to dry out and become grassland if climate change continues unchecked.


Climate models project rising temperatures in most land and ocean regions, featuring more heatwaves and more prolonged periods of heat. Extreme weather events will become more frequent and severe. Heavier and more prolonged periods of rainfall are predicted in most inhabited regions, with more intense, more frequent, and more prolonged drought in some other parts of the world. Climatic effects vary significantly according to region: Mediterranean, sub-Saharan Africa and Indian Ocean/Pacific Island States will be worst affected. Limiting global warming to 1.5°C rather than 2°C could prevent more than 400 million people from being exposed to severe heatwaves, and halve the numbers affected by water shortage.

Why Focus on 1.5°C?

Confronted by the gloomy projections of the IPCC’s Fifth Assessment Report, an overwhelming majority of nations signed up to the Paris Agreement of December 2015, whose goal was to limit global temperature rise to 1.5°C. Scientists believed that this figure was the only climate action target that could stabilize global warming without risking too much damage to the planet.

The signatories also asked the IPCC to compile a Special Report on the effects of global warming of 1.5°C along with advice about how this level would impact on global CO2 emissions.

Special Report on Global Warming - Climate Tipping Point.
The graph indicates we will reach 1.5 degrees by 2040 at current rates of emissions. Source: IPCC SR15 Report.

How long before we reach 1.5°C? Temperatures exceeded 1°C above pre-industrial levels (1850–1900) during the writing of this Special Report. If the current rate of warming continues, the world will reach the 1.5°C level around 2040.

Can We Limit Global Warming To 1.5°C?

There is no guaranteed way to limit global temperature rise to 1.5°C. However, the IPCC’s Special Report identifies two main pathways to consider. One stabilizes global temperature at around 1.5°C. Another sees temperature exceed 1.5°C on a temporary basic before coming back down. Unfortunately, the CO2 emissions that countries have pledged through the NDCs (nationally determined contributions) negotiated as part of the Paris Agreement, will not be enough to limit the rise to 1.5°C.

Special Report on Global Warming - IPCC 1.5 Degrees Pathways
Two main pathways for limiting global temperature rise to 1.5°C above pre-industrial levels. Source: IPCC SR15 Report.

A different set of climate targets are needed to achieve this, such as those underpinning the RCPs (representative concentration pathways) outlined in the IPCC’s Fifth Assessment Report.

Criticism And Doubts

Climate experts are worried about several issues raised (and not raised) by the IPCC’s Special Report.


To achieve 1.5°C – the only remotely safe outcome – carbon emissions must be cut by 45 percent by 2030 and come down to zero by 2050. Since countries usually plan 5-10 years ahead, if the 45 percent carbon cut by 2030 is to be met then plans need to be on the table by the end of 2020. But far from gearing up, key countries seem content to drag their feet: last December – for reasons of self interest – the US, Saudi Arabia, Kuwait and Russia blocked the IPCC’s special report from UN talks. 5

Jim Skea, a co-chair of SR15’s working group on climate change mitigation, agreed that the main problem was the need for urgency. He said that although good progress has been made in the adoption of renewable energy, continuing deforestation was turning natural carbon sinks into sources of CO2 emissions. Furthermore, carbon capture and storage projects – essential techniques for lowering emissions in the concrete and waste disposal industries – have also ground to a halt. 6 For more on this, see: Our Climate Plan Can’t Cope.


Bob Ward, of the Grantham Research Institute on Climate Change expressed surprise that while the report indicates that warming would have very damaging impacts on many parts of the world, it did not mention the likely increase in numbers of climate-driven refugees, a potential “threat multiplier” which could destabilize whole regions leading to increased risks of political instability and conflict. 7


According to the United Nations, world population is predicted to rise by 5 billion this century (from 6.1 billion to 11.2 billion). An increase of about 83 percent in a single century. 8 Surely this is going to have a massive impact on the need for economic growth and development, and thus on energy consumption as well as scarcity of resources.

Last Word

UN Secretary-General Antonio Guterres aptly summed up the situation when he warned: “This Special Report on Global Warming by the world’s leading climate scientists is an ear-splitting wake-up call to the world. It confirms that climate change is running faster than we are – and we are running out of time,” he declared.


  1. IPCC Special Report on Global Warming of 1.5°C (SR15) [][][][][][][][][][]
  2. Special Report on Global Warming of 1.5°C. Incheon, Republic of Korea: Intergovernmental Panel on Climate Change. IPCC Press Release. October 8, 2018. []
  3.  In-depth Q&A: The IPCC’s special report on climate change at 1.5C []
  4.  “IPCC issues Special Report on Global Warming of 1.5°C.” World Meteorological Organization (WMO). []
  5. “Climate change: 12 years to save the planet? Make that 18 months.” Matt McGrath. BBC News. 24 July 2019. []
  6. We have 12 years to limit climate change catastrophe, warns UN.” Jonathan Watts. The Guardian. Oct 8, 2018. []
  7.  “The IPCC global warming report spares politicians the worst details.” Bob Ward. The Guardian. Oct 8, 2018. []
  8. The U.N.’s median estimate predicts the population reaching 8.6 billion in 2030, 9.8 billion in 2050 and 11.2 billion by 2100. “World Population Prospects: The 2017 Revision“. []
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