- Global warming of 2 degrees Celsius above pre-industrial levels poses greater risks than previously believed. These risks can be substantially reduced by limiting warming to 1.5 degrees
- Limiting warming to 1.5 degrees C requires dramatic emission reductions by 2030 and carbon neutrality by around 2050. This would entail unprecedented transformations of energy, land, urban, and industrial systems, including measures to achieve “negative emissions” by removing carbon from the atmosphere.
- Adaptation efforts are currently insufficient to prevent losses associated with 1.5 degrees C warming, but can be significantly increased to reduce the negative consequences of climate change.
What is the IPCC and why is it important?
The Intergovernmental Panel on Climate Change (IPCC) is the leading international body for the assessment of climate change. It was established by the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) in 1988 to provide the world with a clear scientific review of the current state of knowledge on climate change.
Thousands of scientists from all over the world volunteer and are selected by governments to review and assess the latest relevant scientific, technical and socio-economic data to understand climate change, its potential impacts, and options for adaptation and mitigation. The IPCC aims to reflect a range of views and expertise in order to publish comprehensive and objective assessments.
The IPCC does not conduct independent research; rather, it convenes experts from around the world every five to seven years to synthesize the latest climate research findings in peer-reviewed scientific and technical literature. The IPCC issued comprehensive assessments in 1990, 1995, 2001, 2007 and 2014. The next assessment report will be released in 2022.
IPCC reports are never policy prescriptive, but the conclusions are relevant to nations, states, and businesses interested in taking steps to limit and adapt to future warming and reduce the costs of climate change.
What is the 1.5-Degree C Special Report?
During the Sixth Assessment cycle, 2016 – 2022, the IPCC is producing three special reports in addition to a new assessment report. The first of these special reports is called Global warming of 1.5 Degrees C. Is it also referred to as the 1.5-Degree Special Report or SR1.5. This special report was requested by governments at the time they adopted the Paris Agreement of 2015.
The Paris Agreement sets a long-term climate mitigation goal of “holding the increase in the global average temperature to well below 2 degrees C above pre-industrial levels and…pursu[ing] efforts to limit the temperature increase to 1.5 degrees C above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change.”
Like other IPCC reports, SR1.5 includes an assessment of the latest scientific understanding of climate change. The process for developing this report was the same as other IPCC reports; namely, technical experts and governments each reviewed the text twice. The report reflects the consensus of a broad community of stakeholders and holds to IPCC’s highly regarded standards for scientific integrity.
There has not been a global assessment of climate science since the last IPCC report in 2014, so some updating is warranted in this fast-evolving field. However, the specific focus of the report is the risks presented by – and the challenges of avoiding – a warming of 1.5 degrees C above pre-industrial levels. The report examines:
- The impacts that 1.5 degrees C warming would have on the environment and human systems
- Different emissions pathways consistent with limiting warming to 1.5 degrees C, including technology, environmental, institutional, and socio-economic considerations
- Current ambition levels compare to the level needed for 1.5 degrees
- The interactions among climate goals, sustainable development, poverty eradication goals, and efforts to reduce inequalities
What does the Special Report say?
The following summarizes the key finding of the report.
The 1.5 degrees C goal in context
Warming as of the end of 2017 was about 1.0 degree C warmer than pre-industrial times. The current rate of warming is about 0.2 degrees C per decade. We are on track to exceed 1.5 degrees C warming between 2030 and 2052 at that rate of emissions, however 1.5 degrees C warming is not yet locked it. Many regions of the world and seasons of the year are experiencing warming greater than the global average. The land area of the Earth is warming faster than the oceans.
Looking forward, there are fewer risks at 1.5 degrees C than 2 degrees C. New scientific evidence since the last assessment report in 2014 indicate that the risks of 2 degrees C warming are greater than previously thought, particularly for threatened systems (e.g., coral reefs) and global economic impacts.
Even the different scenarios that result in 1.5 degrees C in the long run, have markedly different impacts. There are fewer risks associated with stabilizing warming at 1.5 degrees C as opposed to overshooting 1.5 degrees C, then lowering emissions (and, consequentially, warming) later in the century.
The report examines in detail how pathways that limit warming to 1.5 degrees C interact with the U.N. Sustainable Development Goals (SDGs). In many cases, actions to reduce emissions also help to achieve the SDGs, but this is not universally true.
Projected climate changes, impacts, and risks of 1.5 degrees C warming
While the difference between 1.5 degrees C and 2 degrees C seem intuitively small, the report stresses that the impacts of warming at these different levels will be visibly, and could be profoundly, different. For example, limiting warming to 1.5 degrees C instead of 2 degrees C substantially lowers the risks of:
- Physical changes like hotter days and nights, heavy precipitation events, droughts, and floods
- Ecological changes like species loss and extinction, in both terrestrial and marine environments
- Disease and fatalities from heat (especially in cities) and vector-borne diseases like malaria and dengue fever
- Reduced cereal crop yield (e.g. wheat, rice), especially in sub-Saharan Africa, Southeast Asia, and Central and South America
- Water stress — notably, the number of people exposed to water stress could be up to 50 percent lower at 1.5 degrees C, compared to 2 degrees C
Impacts on the oceans are different at the different warming levels as well. At 1.5 degrees C warming, the Arctic is expected to see an ice-free summer about once every 100 years and global sea levels will rise 0.26 – 0.77 meters (8.7 – 30.3 inches) by 2100. At 2 degrees C, in contrast, ice-free summers in the Arctic could happen once every 10 years, sea levels will rise an additional 0.1 meters (4 inches) by 2100, and there is a substantially higher risk of loss of fisheries, corals, and other damaging changes in marine ecosystems. Coral reefs, in particular, could practically vanish under 2 degrees C (>99% loss), but maintain 10 – 30% of their current abundance at 1.5 degrees C warming.
Moreover, the report adds clarity to how the warming will be distributed to different regions and communities. Land areas (where people live) will warm more than the oceans, so that inhabited regions of the Earth may experience hot days that are about 3 degrees C (5.4 degrees F) warmer than pre-industrial times. Impacts will be disproportionately felt by disadvantaged and vulnerable populations, some indigenous peoples, and communities dependent on agriculture or coastal livelihoods.
The state of global climate adaptation
The report assesses the climate vulnerability of the global energy sector, land and ecosystems, urban environments, the industrial sector, and transportation systems. It concludes that additional adaptation measures are required in all of these sectors, and that the adaptation needs at 1.5 degrees C warming are lower than at 2 degrees C warming. It also highlights that there are limits to adaptive capacity even at 1.5 degrees C warming, and that associated climate losses will occur.
The report finds that it is possible for adaptation investments to alleviate the impacts of climate change. Some of the noted adaptation options are:
- Ecosystem restoration and avoided deforestation
- Efficient irrigation
- Coastal defense and hardening
- Green infrastructure in urban environments
- Risk spreading and sharing (e.g., insurance) and disaster risk management
Many aspects of sustainable development are synergistic with limiting warming to 1.5 degrees C, but they must be properly managed and implemented to avoid maladaptations.
Pathways to 1.5 degrees C
An emissions pathway is a scenario of future global economic output and climate system response. This report does not examine a business-as-usual projection of trends, nor does it forecast likely pathways. Rather, it develops and compares multiple emissions pathways that would limit long-term global warming to 1.5 degrees C in 2100 (some pathways overshoot this target and then return to it in later years). This approach allows a comparison of different portfolios of technologies and behaviors that would all achieve the same goal, as well as the impact of different mitigation timelines for non-CO2 greenhouse gases (so-called short-lived climate pollutants or SLCPs). The comparison provides insight into how sustainable development goals are affected.
The 1.5 degrees C-consistent pathways have several commonalities:
- They require far-reaching and historically unprecedented transformations of energy, land, urban, and industrial systems in the next 20 years.
- They all achieve net zero CO2 emissions (carbon neutrality) by mid-century
- They all rapidly reduce SLCPs, especially methane and black carbon
- They all rely on carbon dioxide removal (CDR) technology, although to differing extents. In pathways with high levels of near-term reductions, less CDR is needed in later years, and the reverse is also true.
- They almost all achieve net negative emissions by the end of the century. The exceptions are pathways that achieve net negative emissions by mid-century; these allow for some increase in emissions through 2100.
The report notes that while we have many different CDR technologies (e.g., afforestation and reforestation, bioenergy with carbon capture and storage (BECCS), direct air capture, and soil sequestration), they each are at different levels of maturity and have different potentials and side effects to consider, including their impact on sustainable development.
The components of the 1.5 degrees C-consistent pathways in the report are consistent with previous analyses of how to limit dangerous global warming: energy demand is substantially reduced through efficiency improvements, electricity comes almost exclusively from non-emitting sources by mid-century, and end uses like transportation and industry are electrified to a large extent. Current land use practices must also shift, including converting potentially hundreds of millions of acres of pasture and agricultural land into energy crops. The report acknowledges the challenges that this level of transition poses to sustainable development.
A key concept in the report is that of a “carbon budget,” the cumulative amount of global greenhouse gas emissions that result in a given level of global warming. The concept of a carbon budget in IPCC reports was first introduced in part of the Fifth Assessment Report (AR5) in 2013. In the context of the 1.5 degrees C goal, the “remaining carbon budget” is the maximum cumulative emissions from 2018 until the year when global net emissions reach zero that would limit warming in 2100 to 1.5 degrees C.
Calculating the remaining carbon budget for a given global warming level requires estimates for two key factors. The first is the warming that has already occurred since pre-industrial times. The second is the climate sensitivity of the Earth—the relationship between emissions and global mean temperature. There are uncertainties in each of these estimates, and those lead to uncertainties in the carbon budget. Additional uncertainties arise from non-CO2 gases and climate tipping points (e.g., permafrost melting and resulting methane release).
The report estimates the remaining carbon budget for a 50% chance of limiting surface air temperature warming to 1.5 degrees C as 580 billion metric tons (Gt) CO2. For a 66% chance of this level of warming the remaining carbon budget is 420 Gt CO2. The carbon budgets are higher for surface temperature warming— 770 Gt CO2 and 570 Gt CO2 for 50% and 66% chance, respectively, of limiting surface warming to 1.5 degrees C. These estimates have very large uncertainties around them (more than 50 percent), but given that annual global emissions are around 42 Gt CO2, the remaining carbon budgets make clear that large cuts are needed in the next decade or two.
While the report lays out the avoided climate damages that come from 1.5 degrees C warming compared to 2 degrees C (see the description of impacts above), it also points out that the mitigation costs to limiting warming to this lower level could be 3-4 times higher than the costs to limit warming to 2 degrees C. In particular, annual average investment needs in the energy system alone are about $2.4 trillion, or about 2.5% of global GDP in 1.5 degrees C-consistent pathways.
How 1.5 degrees C pathways compare with current ambition
The report agrees with other analysis that the first round of nationally determined contributions (NDCs) pledged by countries under the Paris Agreement will lead to more than 1.5 degrees C warming. It goes further to estimate that the emissions pathway associated with current NDCs will lead to 3 degrees C warming in 2100, with additional warming after that.=
The report clearly states that limiting warming to 1.5 degrees C will require strengthened efforts and international cooperation among governments, civil society, and local communities.
What comes next?
With the release of SR1.5, the global community has a clearer, more up-to-date picture of what a 1.5 degrees C warmer world looks like. This new understanding is not radically different from what we’ve known for many years. It paints a picture of rising seas, hotter heat waves, and more frequent and intense severe weather. But it does sharpen our understanding that climate change impacts will come sooner and with more severity than previously thought.
The special report sees many climate solutions as well. Technologies like renewable energy, carbon capture, nuclear energy, electric vehicles, energy storage, and many others all have a role to play in reducing greenhouse gas emissions and putting us on the road to global carbon neutrality.
The report’s findings will inform the Talanoa Dialogue, a process concluding at COP 24 in Katowice, Poland, that is assessing collective progress toward the Paris Agreement’s long-term goals, as a prelude to governments presenting updated NDCs in 2020.