SPM 1. Observed Changes and their Causes
Human influence on the climate system is clear, and recent anthropogenic emissions of greenhouse
gases are the highest in history. Recent climate changes have had widespread impacts
on human and natural systems. {1}
SPM 1.1 Observed changes in the climate system
Warming of the climate system is unequivocal, and since the 1950s, many of the observed
changes are unprecedented over decades to millennia. The atmosphere and ocean have
warmed, the amounts of snow and ice have diminished, and sea level has risen. {1.1}
SPM1.2 Anthropogenic greenhouse gas emissions have increased since the pre-industrial era, driven
largely by economic and population growth, and are now higher than ever. This has led to atmospheric
concentrations of carbon dioxide, methane and nitrous oxide that are unprecedented in
at least the last 800,000 years. Their effects, together with those of other anthropogenic drivers,
have been detected throughout the climate system and are extremely likely to have been
the dominant cause of the observed warming since the mid-20th century. {1.2, 1
In recent decades, changes in climate have caused impacts on natural and human systems on
all continents and across the oceans. Impacts are due to observed climate change, irrespective
of its cause, indicating the sensitivity of natural and human systems to changing climate.
{1.3.2}
SPM 1.4 Changes in many extreme weather and climate events have been observed since about 1950.
Some of these changes have been linked to human influences, including a decrease in cold temperature
extremes, an increase in warm temperature extremes, an increase in extreme high sea
levels and an increase in the number of heavy precipitation events in a number of regions. {1.4}
SPM 2. Future Climate Changes, Risks and Impacts
Continued emission of greenhouse gases will cause further warming and long-lasting
changes in all components of the climate system, increasing the likelihood of severe,
pervasive and irreversible impacts for people and ecosystems. Limiting climate change would
require substantial and sustained reductions in greenhouse gas emissions which, together
with adaptation, can limit climate change risks. {2}
SPM 2.1 Key drivers of future climate
Cumulative emissions of CO2 largely determine global mean surface warming by the late
21st century and beyond. Projections of greenhouse gas emissions vary over a wide range,
depending on both socio-economic development and climate policy. {2.
SPM 2.2 Projected changes in the climate system
Surface temperature is projected to rise over the 21st century under all assessed emission
scenarios. It is very likely that heat waves will occur more often and last longer, and that
extreme precipitation events will become more intense and frequent in many regions. The
ocean will continue to warm and acidify, and global mean sea level to rise. {2.2
SPM 2.3 Future risks and impacts caused by a changing climate
Climate change will amplify existing risks and create new risks for natural and human systems.
Risks are unevenly distributed and are generally greater for disadvantaged people and
communities in countries at all levels of development. {2.3
SPM 2.4 Climate change beyond 2100, irreversibility and abrupt changes
Many aspects of climate change and associated impacts will continue for centuries, even if
anthropogenic emissions of greenhouse gases are stopped. The risks of abrupt or irreversible
changes increase as the magnitude of the warming increases. {2.4
SPM 3. Future Pathways for Adaptation, Mitigation and Sustainable Development
Adaptation and mitigation are complementary strategies for reducing and managing the risks
of climate change. Substantial emissions reductions over the next few decades can reduce climate
risks in the 21st century and beyond, increase prospects for effective adaptation, reduce
the costs and challenges of mitigation in the longer term and contribute to climate-resilient
pathways for sustainable development. {3.2, 3.3, 3.4}
SPM 3.1 Foundations of decision-making about climate change
Effective decision-making to limit climate change and its effects can be informed by a wide
range of analytical approaches for evaluating expected risks and benefits, recognizing the
importance of governance, ethical dimensions, equity, value judgments, economic assessments
and diverse perceptions and responses to risk and uncertainty. {3.
SPM 3.2 Climate change risks reduced by mitigation and adaptation
Without additional mitigation efforts beyond those in place today, and even with adaptation,
warming by the end of the 21st century will lead to high to very high risk of severe, widespread
and irreversible impacts globally (high confidence). Mitigation involves some level
of co-benefits and of risks due to adverse side effects, but these risks do not involve the
same possibility of severe, widespread and irreversible impacts as risks from climate change,
increasing the benefits from near-term mitigation efforts. {3.2, 3.4}
SPM 3.3 Characteristics of adaptation pathways
Adaptation can reduce the risks of climate change impacts, but there are limits to its effectiveness,
especially with greater magnitudes and rates of climate change. Taking a longerterm
perspective, in the context of sustainable development, increases the likelihood that
more immediate adaptation actions will also enhance future options and preparedness. {3.3}
SPM 3.4 Characteristics of mitigation pathways
There are multiple mitigation pathways that are likely to limit warming to below 2°C relative
to pre-industrial levels. These pathways would require substantial emissions reductions over
the next few decades and near zero emissions of CO2 and other long-lived greenhouse gases
by the end of the century. Implementing such reductions poses substantial technological, economic,
social and institutional challenges, which increase with delays in additional mitigation
and if key technologies are not available. Limiting warming to lower or higher levels involves
similar challenges but on different timescales. {3.4
SPM 4. Adaptation and Mitigation
Many adaptation and mitigation options can help address climate change, but no single
option is sufficient by itself. Effective implementation depends on policies and cooperation at
all scales and can be enhanced through integrated responses that link adaptation and mitigation
with other societal objectives. {4}
SPM 4.1 Common enabling factors and constraints for adaptation and mitigation responses
Adaptation and mitigation responses are underpinned by common enabling factors. These
include effective institutions and governance, innovation and investments in environmentally
sound technologies and infrastructure, sustainable livelihoods and behavioural and lifestyle
choices. {4.1}
SPM 4.2 Response options for adaptation
Adaptation options exist in all sectors, but their context for implementation and potential to
reduce climate-related risks differs across sectors and regions. Some adaptation responses
involve significant co-benefits, synergies and trade-offs. Increasing climate change will
increase challenges for many adaptation options. {4.2
SPM 4.3 Response options for mitigation
Mitigation options are available in every major sector. Mitigation can be more cost-effective
if using an integrated approach that combines measures to reduce energy use and the greenhouse
gas intensity of end-use sectors, decarbonize energy supply, reduce net emissions and
enhance carbon sinks in land-based sectors. {4.3
SPM 4.4 Policy approaches for adaptation and mitigation, technology and finance
Effective adaptation and mitigation responses will depend on policies and measures across
multiple scales: international, regional, national and sub-national. Policies across all scales
supporting technology development, diffusion and transfer, as well as finance for responses
to climate change, can complement and enhance the effectiveness of policies that directly
promote adaptation and mitigation. {4.4
SPM 4.5 Trade-offs, synergies and interactions with sustainable development
Climate change is a threat to sustainable development. Nonetheless, there are many opportunities
to link mitigation, adaptation and the pursuit of other societal objectives through integrated
responses (high confidence). Successful implementation relies on relevant tools, suitable
governance structures and enhanced capacity to respond (medium confidence). {3.5, 4.5}
http://www.ipcc.ch/pdf/assessment-report/ar5/syr/AR5_SYR_FINAL_SPM.pdf
