Transformative collective actions to limit and adapt to human-caused climate change are urgently needed to protect current and future life on Earth and promote well-being, global equity, and safety.

The Challenge

The climate crisis, which has been unequivocally driven by human activities that result in increased emissions of greenhouse gases (GHGs),^[i] is proving increasingly costly and disruptive for the world. The responsibility for and the impacts of the crisis are distributed unequally among different regions, populations, and sectors. Overall, the societal response has been insufficient in scale and too slow to avert disastrous impacts. To reduce loss of life, suffering, and worsened inequities, faster and more comprehensive actions must be taken on both mitigation of the causes and adaptation to the effects. Strategic, efficient, and inclusive climate actions can lead to greater equity, well-being, and security, and protect the human right to a healthy and sustainable environment.^[ii]

The Evidence and Projections for Natural Systems

As a result of burning fossil fuels and other human activities over the past century, atmospheric GHG concentrations^[iii] have risen to levels unprecedented in at least the last 800,000 years (in the case of CO₂, in at least the last 2 million years).^[iv] The global average surface temperature has reached 1.1°C above 1850-1900 in 2011-2020, and will continue to rise.^[v] 2011-2020 was the warmest decade in the history of modern civilization, and each decade since the 1990s has been warmer than previous decades.^[vi]

The degree of warming that will occur in the coming decades, and resulting risks to life on Earth, will depend primarily on the choices that organizations and individuals across society make now about future emissions and CO₂ removal from the atmosphere. Global average temperatures will only stabilize after CO₂ emissions are matched by the amount removed (net-zero).^[vii] Limiting the overall increase in average temperature to 1.5°C requires achieving net-zero CO₂ emissions by around 2050^[viii] or even sooner if warming temperatures reduce the ability of nature to absorb and retain carbon.^[ix] Gradual decline in average temperatures after a peak will require both net negative CO₂ emissions and large reductions in emissions of other short-lived climate pollutants, such as methane, hydrofluorocarbons, and black carbon.^[x] Even if the global temperature stabilizes, the delayed response of ocean warming and ice sheet melt to atmospheric temperatures means sea level will continue to rise for centuries or millennia, although the rise will occur much more slowly than if warming continues.^[xi]

Many other changes related to warming and increased atmospheric CO₂ concentrations have already been observed and are expected to continue: extreme events that are more frequent, more intense, or both (e.g., heat waves, heavy rainfall, tropical cyclones, drought, wildfires); reductions in ice and snow in the Arctic sea, Northern Hemisphere, Greenland, West Antarctica, and mountain glaciers; rising sea level; changes in the global water cycle; toxic algae; changes in the growth and nutritional value of land plants; and acidification of ocean waters.^[xii] Further global warming increases risk of reaching climate tipping points, which are critical thresholds beyond which a system reorganizes, often abruptly and/or irreversibly, such as ice-sheet collapse and rainforest dieback.^[xiii] The changing climate is increasingly altering landscapes and severely stressing the world’s ecosystems, leading to increasing and extraordinary numbers of extinctions on land and in the oceans.^[xiv]

The Consequences for Humans

Humanity faces profound challenges due to the current and projected impacts of climate change.^[xv] The changing climate will increasingly threaten food, water, and energy security,^[xvi] and further increase deaths, illnesses, and injuries directly related to extreme climate events, as well as climate-sensitive diseases transmitted by water, soil, air, and insects.^[xvii] Environmental degradation and pollution caused by extreme climate events will continue to impact human health.^[xviii] The impacts of climate change on ecosystems and communities will continue to adversely affect mental health and profoundly alter cultural and spiritual traditions of Indigenous and local communities in tangible and intangible ways.^[xix]

Economic disruption will result from shifts in agricultural and fisheries productivity; submergence and loss of land due to sea-level rise; diminished labor productivity; disruption in education systems; damages to critical infrastructure; and decreases in air, water, and soil quality.^[xx] Economic and social disruptions are already driving migration and population displacement, which will further increase and remain inequitable in the absence of just policies and interventions.^[xxi] Insecurity and compound risks, including the increased potential for conflict and instability, will increasingly stress every region and sector worldwide.^[xxii]

Extremes and impacts are not uniform across regions and populations.^[xxiii] The distribution of risk moves through specific communities and people via pre-existing systematic inequities, such as poverty, gender discrimination, settler colonialism, and racialized histories of property regimes, as examples.^[xxiv] Without just interventions, pre-existing inequities will be exacerbated by disparities caused by climate change and by unjust climate mitigation and adaptation actions.^[xxv] Adaptation measures, while critical, cannot prevent all losses and damages, which will continue to be unequally distributed and concentrated among the poorest and most vulnerable populations.^[xxvi]

The Needed Responses

Addressing the destructive consequences of climate change requires that governments, industry, the financial sector, academia, and other organizations advance transformative mitigation and adaptation actions simultaneously. Many actions have health and economic co-benefits.^[xxvii] Transformative actions to undertake include: using energy more efficiently; transitioning to renewable energy sources and products and services that do not release GHGs; taking fast action on short-lived climate pollutants;^[xxviii] implementing technologies and practices to remove and store CO₂ from the atmosphere; and adapting to unavoidable changes.^[xxix] Actions are needed across the globe, with attention to local variation and tradeoffs, striving to alleviate rather than exacerbate pre-existing injustices and inequities.^[xxx] To equitably distribute accountability for action, greater financial responsibility for implementing adaptation measures, and for covering the costs of unavoidable losses and damages, should fall on those whose historic emissions have been the greatest.^[xxxi]

Effective climate risk governance requires support for solutions-oriented and community-based research and engagement of scientists with policy practitioners, communities, businesses, and the public.^[xxxii] Diverse ways of knowing, including Indigenous knowledge, local knowledge, and Western scientific knowledge, should be brought together to address the crisis.^[xxxiii] Scientists can provide allyship to community organizing and social movements, including those led by youth and Indigenous and ethnic communities, which can foster hope, prioritize climate justice, and drive cultural and policy changes.^[xxxiv]

Collective actions to mitigate and adapt to the climate crisis are urgently needed to protect life on Earth and, if truly transformative and just, can yield significant benefits for current and future generations.

^[i] According to the IPCC 6th Assessment Report (2023; Summary for Policymakers): “Human activities, principally through emissions of greenhouse gases, have unequivocally caused global warming, with global surface temperature reaching 1.1°C above 1850-1900 in 2011-2020.”

^[ii] Following the UN Resolution adopted 2022, The human right to a clean, healthy and sustainable environment.

^[iii] Including CO₂, methane, nitrous oxide, halocarbons, and black carbon.

^[iv] According to the IPCC 6th Assessment Report (2023; Summary for Policymakers): “In 2019, atmospheric CO₂ concentrations (410 parts per million) were higher than at any time in at least 2 million years, and concentrations of methane (1866 parts per billion) and nitrous oxide (332 parts per billion) were higher than at any time in at least 800,000 years.”

^[v] According to the IPCC 6th Assessment Report (2023; Summary for Policymakers): “Human activities, principally through emissions of greenhouse gases, have unequivocally caused global warming, with global surface temperature reaching 1.1°C above 1850-1900 in 2011-2020. Global greenhouse gas emissions have continued to increase, with unequal historical and ongoing contributions arising from unsustainable energy use, land use and land-use change, lifestyles and patterns of consumption and production across regions, between and within countries, and among individuals (high confidence)”

^[vi] According to the World Meteorological Organization (2023; The Global Climate 2011-2020): A decade of accelerating climate change), 2011-2020 “was the warmest decade on record by a clear margin for both land and ocean” and “each successive decade since the 1990’s has been warmer than all previous decades.”

^[vii] Net zero means the amount of CO₂ that humans emit into the atmosphere is matched by the amount removed by natural or technological means.  According to the IPCC 6th Assessment Report (2023; Summary for Policymakers): “...reaching net zero anthropogenic CO₂ emissions is a requirement to stabilize human-induced global temperature increase at any level"

^[viii] According to the IPCC Special Report: Global Warming of 1.5°C (2018; Summary for Policymakers): “In model pathways with no or limited overshoot of 1.5°C, global net anthropogenic CO2 emissions decline by about 45% from 2010 levels by 2030 (40–60% interquartile range), reaching net zero around 2050 (2045–2055 interquartile range)." ...here: https://www.ipcc.ch/sr15/chapter/spm/

^[ix] According to the IPCC 6th Assessment Report (2023; Longer Report): “Limiting human-caused global warming requires net zero anthropogenic CO₂ emissions. Pathways consistent with 1.5°C and 2°C carbon budgets imply rapid, deep, and in most cases immediate GHG emission reductions in all sectors (high confidence). Exceeding a warming level and returning (i.e., overshoot) implies increased risks and potential irreversible impacts; achieving and sustaining global net negative CO₂ emissions would reduce warming (high confidence).”

^[x] According to the IPCC 6th Assessment Report (2023; Longer Report): “Global modelled pathways that reach and sustain net zero GHG emissions are projected to result in a gradual decline in surface temperature (high confidence). Reaching net zero GHG emissions primarily requires deep reductions in CO₂, methane, and other GHG emissions, and implies net negative CO₂ emissions.”

^[xi] According to the IPCC 6th Assessment Report (2023; Longer Report): “Sea level rise is unavoidable for centuries to millennia due to continuing deep ocean warming and ice sheet melt, and sea levels will remain elevated for thousands of years (high confidence).”

^[xii] Observed impacts and changes to climate systems are referenced at length here: IPCC 6th Assessment Report (2023; Longer Report, page 12, 2.1.2. Observed Climate System Changes and Impacts to Date)

^[xiii] Definition of tipping points is sourced from the IPCC 6th Assessment Report (2023; Annex 1, Glossary). The recent Global Tipping Points Report (led by the University of Exeter’s Global Systems Institute with the support of more than 200 researchers from over 90 organizations in 26 countries) identified five major Earth system tipping points already at risk of being crossed due to the present level of global warming (related to the Greenland and West Antarctic ice sheets, warm-water coral reefs, North Atlantic Subpolar Gyre circulation, and permafrost regions), and three more tipping points threatened to be crossed in the 2030s as the world exceeds 1.5^oC global warming.”

^[xiv] According to the IPCC 6th Assessment Report (2023; Longer Report): “As warming levels increase, so do the risks of species extinction or irreversible loss of biodiversity in ecosystems such as forests (medium confidence), coral reefs (very high confidence) and in Arctic regions (high confidence).”

^[xv] According to the IPCC 6th Assessment Report (2023; Summary for Policymakers): “Human-caused climate change is already affecting many weather and climate extremes in every region across the globe. This has led to widespread adverse impacts and related losses and damages to nature and people (high confidence).”

^[xvi] According to the IPCC 6th Assessment Report (2023; Summary for Policymakers): “Climate change has reduced food security and affected water security, hindering efforts to meet Sustainable Development Goals (high confidence).”

^[xvii] According to the IPCC 6th Assessment Report (2023; Summary for Policymakers): “In all regions increases in extreme heat events have resulted in human mortality and morbidity (very high confidence). The occurrence of climate-related food-borne and water-borne diseases (very high confidence) and the incidence of vector-borne diseases (high confidence) have increased.” Also according to the IPCC 6th Assessment Report (2023; Summary for Policymakers): “In the near term, every region in the world is projected to face further increases in climate hazards (medium to high confidence, depending on region and hazard), increasing multiple risks to ecosystems and humans (very high confidence). Hazards and associated risks expected in the near term include an increase in heat-related human mortality and morbidity (high confidence), food-borne, water-borne, and vector-borne diseases (high confidence), and mental health challenges.”

^[xviii] According to the IPCC 6th Assessment Report (Climate Change 2022: Impacts, Adaptation and Vulnerability): “It is well established that climate change compounds the impacts of pressures that humans place on the environment (high confidence) and that environmental degradation can undermine options for adaptation and an enabling environment, with poor and natural resource-dependent groups most acutely affected.”

^[xix] According to the IPCC 6th Assessment Report (2023; Summary for Policymakers): “In assessed regions, some mental health challenges are associated with increasing temperatures (high confidence), trauma from extreme events (very high confidence), and loss of livelihoods and culture (high confidence).”

^[xx] According to the IPCC 6th Assessment Report (2023; Summary for Policymakers): “Economic damages from climate change have been detected in climate-exposed sectors, such as agriculture, forestry, fishery, energy, and tourism. Individual livelihoods have been affected through, for example, destruction of homes and infrastructure, and loss of property and income, human health and food security, with adverse effects on gender and social equity. (high confidence)”

^[xxi] According to the IPCC 6th Assessment Report (2023; Summary for Policymakers): “Climate and weather extremes are increasingly driving displacement in Africa, Asia, North America (high confidence), and Central and South America (medium confidence), with small island states in the Caribbean and South Pacific being disproportionately affected relative to their small population size (high confidence).”

^[xxii] According to the IPCC 6th Assessment Report (2023; Summary for Policymakers): With further warming, climate change risks will become increasingly complex and more difficult to manage. Multiple climatic and non-climatic risk drivers will interact, resulting in compounding overall risk and risks cascading across sectors and regions. Climate-driven food insecurity and supply instability, for example, are projected to increase with increasing global warming, interacting with non-climatic risk drivers such as competition for land between urban expansion and food production, pandemics and conflict. (high confidence).

[xxiii] According to the IPCC 6th Assessment Report (2023; Summary for Policymakers): “Climate change has caused widespread adverse impacts and related losses and damages to nature and people that are unequally distributed across systems, regions and sectors.”

^[xxiv] According to the IPCC 6th Assessment Report (Climate Change 2022: Impacts, Adaptation and Vulnerability): “Vulnerability at different spatial levels is exacerbated by inequity and marginalization linked to gender, ethnicity, low income or combinations thereof (high confidence), especially for many Indigenous Peoples and local communities (high confidence). Present development challenges causing high vulnerability are influenced by historical and ongoing patterns of inequity such as colonialism, especially for many Indigenous Peoples and local communities (high confidence).” And, “The intersection of gender with race, class, ethnicity, sexuality, Indigenous identity, age, disability, income, migrant status and geographical location often compounds vulnerability to climate change impacts (very high confidence), exacerbates inequity and creates further injustice (high confidence). There is evidence that present adaptation strategies do not sufficiently include poverty reduction and the underlying social determinants of human vulnerability such as gender, ethnicity and governance (high confidence).”

^[xxv] According to the IPCC 6th Assessment Report (2023; Longer Report): “Prioritising equity, climate justice, social justice, inclusion and just transition processes can enable adaptation and ambitious mitigation actions and climate resilient development. Adaptation outcomes are enhanced by increased support to regions and people with the

highest vulnerability to climatic hazards. Integrating climate adaptation into social protection programs improves resilience.”

^[xxvi] According to the IPCC 6th Assessment Report (2023; Longer Report): “Adaptation does not prevent all losses and damages, even with effective adaptation and before reaching soft and hard limits (high confidence).”

^[xxvii] According to the IPCC 6th Assessment Report (2023; Longer Report): “Mitigation and adaptation options can lead to synergies and trade-offs with other aspects of sustainable development. Synergies and trade-offs depend on the pace and magnitude of changes and the development context including inequalities, with consideration of climate justice. The potential or effectiveness of some adaptation and mitigation options decreases as climate change intensifies. (high confidence) In the energy sector, transitions to low-emission systems will have multiple co-benefits, including improvements in air quality and health. There are potential synergies between sustainable development and, for instance, energy efficiency and renewable energy. (high confidence)”

^[xxviii] According to the IPCC 6th Assessment Report (2023; Summary for Policymakers): “GHG emissions reductions by 2030 and 2040, particularly reductions of methane emissions, lower peak warming, reduce the likelihood of overshooting warming limits and lead to less reliance on net negative CO2 emissions that reverse warming in the latter half of the century.”

^[xxix] Other climate intervention approaches, such as solar radiation management, require further research and cautious consideration of risks. See AGU Position Statement on Climate Intervention (revised and reaffirmed April 2023). Climate interventions cannot substitute for deep cuts in emissions or the need for adaptation.

^[xxx] According to the IPCC 6th Assessment Report (2023; Summary for Policymakers): ^“Adaptation and mitigation actions that prioritise equity, social justice, climate justice, rights-based approaches, and inclusivity, lead to more sustainable outcomes, reduce trade-offs, support transformative change and advance climate resilient development. Redistributive policies across sectors and regions that shield the poor and vulnerable, social safety nets, equity, inclusion and just transitions, at all scales can enable deeper societal ambitions and resolve tradeoffs with sustainable development goals. Attention to equity and broad and meaningful participation of all relevant actors in decision making at all scales can build social trust which builds on equitable sharing of benefits and burdens of mitigation that deepen and widen support for transformative changes.”

^[xxxi] According to the IPCC 6th Assessment Report (2023; Summary for Policymakers): “Adaptation does not prevent all losses and damages, even with effective adaptation and before reaching soft and hard limits. Losses and damages are across systems, regions and sectors and are not comprehensively addressed by current financial, governance and institutional arrangements, particularly in vulnerable developing countries. With increasing global warming, losses and damages increase and become increasingly difficult to avoid, while strongly concentrated among the poorest vulnerable populations.” According to the IPCC 6th Assessment Report (2023; Longer Report): “There is improved understanding of both economic and non-economic losses and damages, which is informing international climate policy and which has highlighted that losses and damages are not comprehensively addressed by current financial, governance and institutional arrangements, particularly in vulnerable developing countries (high confidence).” See also the decision adopted during COP 28 to operationalize a Loss and Damage fund (FCCC/CP/2023/L.1).

^[xxxii] See also: AGU Position Statement on Resilience (revised and reaffirmed August 2022).

^[xxxiii] According to the IPCC 6th Assessment Report (Climate Change 2022: Impacts, Adaptation and Vulnerability): “Enhancing knowledge on risks, impacts, and their consequences, and available adaptation options promotes societal and policy responses (high confidence). A wide range of top-down, bottom-up and co-produced processes and sources can deepen climate knowledge and sharing, including capacity building at all scales, educational and information programmes, using the arts, participatory modelling and climate services, Indigenous knowledge and local knowledge and citizen science (high confidence). These measures can facilitate awareness, heighten risk perception and influence behaviours (high confidence).”

^[xxxiv] According to the IPCC 6th Assessment Report (2023; Technical Summary): “Climate-induced changes are not experienced equally across genders, income levels, classes, ethnicities, ages or physical abilities (high confidence). Therefore, participation of historically excluded groups, such as women, youth and marginalised communities (e.g., Indigenous Peoples, ethnic minorities, the disabled and low-income households), contributes to more equitable and socially just adaptation actions.”