The world if we limit warming to 2 degrees... or if we emit a lot more greenhouse gases
The world’s leading climate scientists have delivered their latest assessment on how climate change is affecting our planet and us, and what’s ahead.
In more than 2,000 pages and 30 chapters, the report by the UN climate panel (IPCC) goes into many fine details - from the impact on coffee beans and tourism to the possibility of civil war.
Here are some key quotes from the summary for policymakers:
1. Climate change is happening now - here, there and everywhere
“In recent decades changes in climate have caused impacts on natural and human systems on all continents and across the oceans.”
“Observed impacts of climate change are widespread and substantial.”
“Many terrestrial, freshwater and marine species have shifted their geographic ranges, seasonal activities, migration patterns, and abundance, and species interactions in response to ongoing climate change (high confidence).”
“Based on many studies covering a broad range of regions and crops, negative impacts of climate change on crop yields have been more common than positive impacts (high confidence).
2. And it’s rapidly getting worse
“Increased tree mortality and associated forest dieback is projected to occur in many regions over the 21st century, due to increased temperatures and drought (medium confidence). Forest dieback poses risks for carbon storage, biodiversity, wood production, water quality, amenity and economic activity.”
“Freshwater-related risks of climate change increase significantly with increasing greenhouse gas concentration (robust evidence, high agreement).”
“Due to climate change by the mid 21st century and beyond, global marine-species redistribution and marine-biodiversity reduction in sensitive regions will challenge the sustained provision of fisheries productivity and other ecosystem services (high confidence).”
“Increasing magnitudes of warming increase the likelihood of severe, pervasive, and challenging irreversible impacts.”
3. It’s not just the polar bears, corals and rainforests that are threatened – it’s us
“People, places, and ecosystems in poor and rich countries around the world are vulnerable and exposed to climate change, in different ways.”
“Impacts from recent climate-related extremes, such as heat waves, droughts, floods, cyclones, and wildfires reveal significant vulnerability and exposure of some ecosystems and many human systems to current climate variability (very high confidence).”
“Climate change is projected to progressively increase inter-annual variability of crop yields in many regions. These projected impacts will occur in the context of rapidly rising crop demand.”
The IPCC identifies eight key risks to humans related to climate change. These include sea level rise, coastal flooding and storm surges; heat waves, drought and rain variability; inland flooding and water shortage; loss of marine and terrestrial ecosystems and their ecosystem services and multiple interacting hazards. These in turn can disrupt food and water supply and lead to loss of homes, livelihoods and cultures; and lead to injury and death.
4. Climate change interacts with other problems we’re causing and struggling with
“A large fraction of both terrestrial and freshwater species faces increased extinction risk under projected climate change during and beyond the 21st century, especially as climate change interacts with other stressors, such as habitat modification, over-exploitation, pollution, and invasive species (high confidence).
“The progressive expansion of oxygen minimum zones and anoxic “dead zones” is projected to further constrain fish habitat. (…) Climate change adds to the threats of overfishing and other non-climatic stressors, this complicating marine management regimes (high confidence).”
“Climate-related hazards exacerbate other stressors, often with negative outcomes for livelihoods, especially for people living in poverty (high confidence).”
5. How bad it will get depends on how much more will we pollute
Scenarios RCP4.5, 6.0, and 8.5 assume we do too little, too late. This is the result:
“Within this century, magnitudes and rates of climate change associated with medium- to high-emission scenarios (RCP4.5, 6.0, and 8.5) pose high risk of abrupt and irreversible regional-scale change in the composition, structure, and function of terrestrial and freshwater ecosystems (including wetlands) (medium confidence). Examples that would lead to substantial impact on climate are the boreal-tundra Arctic system (medium confidence) and the Amazon forest (low confidence). These regional-scale changes would lead to substantial additional climate change.”
“For medium- to high-emission scenarios (RCP4.5, 6.0 and 8.5) ocean acidification poses substantial risks to marine ecosystems, especially polar ecosystems and coral reefs, associated with impacts on the physiology, behavior, and population dynamics of individual species from phytoplankton to animals (medium to high confidence).”
"Climate change over the 21st century is projected to reduce renewable surface water and groundwater resources significantly in most dry subtropical regions (robust evidence, high agreement), intensifying competition for water among sectors (limited evidence, medium agreement)."
“The precise levels of climate change sufficient to trigger tipping points (thresholds for abrupt and irreversible change) remain uncertain, but the likelihood of risk associated with crossing tipping points in the earth system or interlinked human and natural systems increases with rising temperature (medium confidence).”
6. And, well, it truly can get bad, threatening our security and fueling conflicts
“Climate change over the 21st century is projected to increase displacement of people (medium evidence, high agreement).”
“Climate change can indirectly increase risks of violent conflicts in the form of civil war and inter-group violence by amplifying well-documented drivers of these conflicts such as poverty and economic shocks (medium confidence). Multiple lines of evidence relate climate variability to these forms of conflict.”
“The impacts of climate change on the critical infrastructure and territorial integrity of many states are expected to influence national security policies (medium evidence, medium agreement). For example, land inundation due to sea-level rise poses risks to the territorial integrity of small-island states and states with extensive coastlines. Some transboundary impacts of climate change, such as changes in sea ice, shared water resources, and pelagic fish stocks, have the potential to increase rivalry among states, but robust national and intergovernmental institutions can enhance cooperation and manage many of these rivalries.”
7. But with faster cuts on climate pollution, risks can be reduced substantially
RCP2.6 scenario assumes we cut emissions enough to limit warming to less than 2 degrees C – the goal governments have agreed to in the UN climate talks:
"The overall risks of climate change impacts can be reduced by limiting the rate and magnitude of climate change. Risks are reduced substantially under the assessed scenario with lowest temperature projections (RCP2.6 – low emissions) compared to the highest temperatures projections (RCP8.5 – high emissions), particularly in the second half of the 21st century (very high confidence)."
“Climate-related risks are much greater with continued high emissions than with ambitious mitigation. Unchecked emissions increase the likelihood of severe and pervasive impact that may be irreversible or unanticipated.”
“Mitigation and adaptation choices in the near-term will affect the risks of climate change throughout the 21st century (high confidence).”
8. And we will need to adapt too
“For the major crops (wheat, rice, and maize) in tropical and temperate regions, climate change without adaptation is projected to negatively impact production for local temperature increases of 2°C or more above late-20th-century levels, although individual locations may benefit (medium confidence).”
“Effective and inclusive climate-change adaptation can help build richer, more resilient world in the near-term and beyond.”
“A first step towards adaptation to future climate change can be reducing vulnerability and exposure to present climate variability (high confidence). “
9. But we can’t count on adaptation alone
“Prospects for climate-resilient pathways for sustainable development are related fundamentally to what the world accomplishes with climate-change mitigation (high confidence).”
“Greater rates and magnitude of climate change increase the likelihood of exceeding adaptation limits (high confidence). Limits to adaptation occur when adaptive actions to avoid intolerable risks for an actor’s objectives or for the needs of a system are not possible or are not currently available.”
10. Nor should we count on simplistic economic models that can’t capture the true costs of climate change
“Global economic impacts from climate change are difficult to estimate. Economic impact estimates completed over the past 20 years vary in their coverage of subsets of economic sectors and depend on a large number of assumptions, many of which are disputable, and many estimates do not account for catastrophic changes, tipping points, and many other factors.”
"Throughout the 21st century, climate-change impacts are projected to slow down economic growth, make poverty reduction more difficult, further erode food security, and prolong existing and create new poverty traps, the latter particularly in urban areas and emerging hotspots of hunger (medium confidence)."
“Some low-lying developing countries and small island states are expected to face very high impacts that, in some cases, could have associated damage and adaptation costs of several percentage points of GDP.”
So what are we going to do about it? That is what the IPCC will discuss in their next report, that will be published on April the 13th, so stay tuned.