IPCC Special Report on Oceans and Cryosphere, The Important Bits

Intergovernmental Panel on Climate Change (IPCC) Report, September 24, 2019
The Ocean and Cryosphere (the icy part of our planet) in a Changing Climate
A Summary of Important Findings

Overall of course, climate change is astonishingly worse with every new report. This one is no exception. Polar and mountain ice are melting faster, the middle estimate of sea level rise is now up to four feet this century, and adaptation limits loom, meaning migration and abandonment will happen sooner rather than later. Caution is also advised with interpretation of this report or any science when risks are high because the science understates. Consensus reports are no exception and are actually understated to a greater degree, relative to recently published science. The reasons are because findings related to rapidly changing trends cannot be fully represented in statistical analyses, obtaining a consensus when evidence discovery is new to science is difficult, and climate modeling is as yet incapable of robustly resolving abrupt changes and collapses. So what this means is that even though this report summarizes what appears to be apocalyptic climate impacts either happening already or projected to happen, in the real world impacts are and will likely be worse and we should plan on worst-case scenario or worse impacts.

The highlights of what I believe are the most important things are presented below, their individual bullets from the Summary for Policy Makers follow. Mostly I have used the words of IPCC authors, simplified a bit when necessary. These are presented in the order that they are presented in the report and are not ranked for importance:

• Permafrost regions are (likely) currently releasing additional net methane and CO2 to the atmosphere due to thaw, meaning permafrost regions have (likely) flipped from sequestration to emissions.
• Arctic sea ice changes in September are likely unprecedented for at least 1,000 years. The area of multi-year ice at least five years old has declined by approximately 90% in the Arctic.
• Nearly 50% of coastal wetlands have been lost over the last 100 years as a result of the combined effects of localised human pressures, sea level rise, warming and extreme climate events. Vegetated coastal ecosystems are already responsible for 2.75 gigatons (Gt) CO2 (equivalents – CO2 and methane) emissions annually.
• By 2100, projected near-surface (up to 13 feet) permafrost area shows a decrease of 24% and 69% for the best and worst-case scenarios, leading to the cumulative release of near 100 billion to near 1,000 billion tons of CO2 to the atmosphere by 2100. We have emitted 2,000 Gt total CO2 in the last 200 years. Global permafrosts contain about 6,000 Gt CO2 or CO2 equivalents including methane.
• The rate of global mean sea level rise is projected to reach up to 20mm (0.75 inch) per year under under the worst-case scenario in 2100, and to exceed several centimetres per year (1.2 inches) in the 22nd century. Model studies indicate multi-meter rise in sea level by 2300 (18 feet for the worst-case scenario.)
• Processes controlling the timing of future ice-shelf loss and the extent of ice sheet collapse could increase Antarctica’s contribution to sea level rise to values substantially higher than the likely range. Considering the consequences of sea level rise that a collapse of parts of the Antarctic Ice Sheet entails, this high impact risk merits attention.
• Extreme sea level events (highest tides) that were 100-year occurrences in our old climate (happen on average every 100 years), will happen every year by 2050.
• The highest mean high water (the average of all high tides) that happened once every 100 years in our old climate will happen every year by 2100.
• Annual coastal flood damages are projected to increase by 2–3 orders of magnitude by 2100 compared to today. Three orders of magnitude is 1,000 times, or 100,000 percent.
• Adaptation limits will be reached in the most critical coastal, coral reef and island areas well before the end of this century, meaning that there will be no alternative except to migrate, relocate, abandon, flee, however one prefers to think of it.
• At global scale, coastal protection can reduce flood risk by 2–3 orders of magnitude during the 21st century, but depends on investments on the order of tens to several hundreds of billions of US$ per year.
• Restoration of vegetated coastal ecosystems, such as mangroves, tidal marshes and seagrass meadows (coastal ‘blue carbon’ ecosystems), could provide climate change mitigation through increased carbon uptake and storage of around 0.5% of current global emissions annually, or 0.2 gigatons of our annual 38 gigatons CO2 emissions. Understand that to just meet the 1.5 C limit to dangerous warming we need 100 percent emissions reductions by mid-century plus 12.5 gigatons of atmospheric carbon dioxide removal annually through nature-based or industrial climate pollution treatment means.
• Expert judgement is required. (This one I am particularly pleased to see included. Because of the understatement in science conundrum I mentioned in the opening paragraph, because of the limits of science, expert judgement should be used to convey risk. This is not science. Science is based in statistically certainty — very different from an opinion of an expert. If we had of done this from the beginning, we very likely would not be in the mess we are in today.) Those stakeholders (individuals, communities, industries or infrastructures, etc.) with higher risk tolerance (e.g., those planning for unforeseen conditions) often prefer to use the “likely” range of projections, while stakeholders with a lower risk tolerance should probably consider sea level rise that is above the upper end of the likely range. This is critically important as most of us are likely in the low risk tolerant group. That is, if we are impacted by sea level rise or extreme high tides, it is likely that we will not be able to adapt and must abandon our non migratable resources.
• Because of sea level rise and ice loss, many nations will face challenges to adapt, even with ambitious mitigation. In a high emissions scenario, many oceanside and polar ice dependent communities are projected to face adaptation limits (e.g. biophysical, geographical, financial, technical, social, political and institutional) during the second half of the 21st century. Because most of us are in low risk tolerant groups and must plan for impacts that are more extreme than the worst-case scenario, our critical thresholds will likely happen mid-century or before.

The bullets from IPCC’s new report Summary for Policy Makers are presented below:

The report can be found here.

From the Summary for Policy Makers —

A1.3 Permafrost temperatures have increased to record high levels (1980s-present) (very high
confidence) including the recent increase by 0.29°C ± 0.12°C from 2007 to 2016 averaged across polar and high mountain regions globally. Arctic and boreal permafrost contain 1460–1600 Gt organic carbon, almost twice the carbon in the atmosphere (medium confidence). There is medium evidence with low agreement whether northern permafrost regions are currently releasing additional net methane and CO2 due to thaw. Permafrost thaw and glacier retreat have decreased the stability of high-mountain slopes (high confidence). {2.2.4, 2.3.2, 3.4.1, 3.4.3, Figure SPM.1}

A1.4 Between 1979 and 2018, Arctic sea ice extent has very likely decreased for all months of the year. September sea ice reductions are very likely 12.8 ± 2.3% per decade. These sea ice changes in September are likely unprecedented for at least 1000 years. Arctic sea ice has thinned, concurrent with a transition to younger ice: between 1979 and 2018, the areal proportion of multi-year ice at least five years old has declined by approximately 90% (very
high confidence). Feedbacks from the loss of summer sea ice and spring snow cover on land have contributed to amplified warming in the Arctic (high confidence) where surface air temperature likely increased by more than double the global average over the last two decades. Changes in Arctic sea ice have the potential to influence mid-latitude weather (medium confidence), but there is low confidence in the detection of this influence for specific weather types. Antarctic sea ice
extent overall has had no statistically significant trend (1979–2018) due to contrasting regional signals and large interannual variability (high confidence). {3.2.1, 6.3.1; Box 3.1; Box 3.2; A1.2, Figures SPM.1, SPM.2}

A6.1 Vegetated coastal ecosystems protect the coastline from storms and erosion and help buffer the impacts of sea level rise. Nearly 50% of coastal wetlands have been lost over the last 100 years, as a result of the combined effects of localised human pressures, sea level rise, warming and extreme climate events (high confidence). Vegetated coastal ecosystems are important carbon stores; their loss is responsible for the current release of 0.04–1.46 GtC yr–1 (medium confidence). In response to warming, distribution ranges of seagrass meadows and kelp forests are expanding at high latitudes and contracting at low latitudes since the late 1970s (high confidence), and in some areas episodic losses occur following heatwaves (medium confidence). Large-scale mangrove mortality that is related to warming since the 1960s has been partially offset by their encroachment into subtropical salt marshes as a result of increase in temperature, causing the loss of open areas with herbaceous plants that provide food and habitat for dependent fauna (high confidence). {4.3.3, 5.3.2, 5.3.6, 5.4.1, 5.5.1, Figure SPM.2}.

B1.4 Widespread permafrost thaw is projected for this century (very high confidence) and beyond. By 2100, projected near-surface (within 3–4 m) permafrost area shows a decrease of 24 ± 16% (likely range) for RCP2.6 and 69 ± 20% (likely range) for RCP8.5. The RCP8.5 scenario leads to the cumulative release of tens to hundreds of
billions of tons (GtC) of permafrost carbon as CO2 and methane to the atmosphere by 2100 with the potential to exacerbate climate change (medium confidence). Lower emissions scenarios dampen the response of carbon emissions from the permafrost region (high confidence). Methane contributes a small fraction of the total additional carbon release but is significant because of its higher warming potential. Increased plant growth is projected to replenish soil carbon in part, but will not match carbon releases over the long term (medium confidence). {2.2.4, 3.4.2, 3.4.3, Figure SPM.1, Cross-Chapter Box 5 in Chapter 1}

B3. Sea level continues to rise at an increasing rate. Extreme sea level events that are historically rare (once per century in the recent past) are projected to occur frequently (at least once per year) at many locations by 2050 in all RCP scenarios,
especially in tropical regions (high confidence). The increasing frequency of high water levels can have severe impacts in many locations depending on exposure (high confidence). Sea level rise is projected to continue beyond 2100 in all RCP scenarios. For a high emissions scenario (RCP8.5), projections of global sea level rise by 2100 are greater than in AR5 due to a larger contribution from the Antarctic Ice Sheet (medium confidence). In coming centuries under RCP8.5, sea level rise is projected to exceed rates of several centimetres per year resulting in multi-metre rise (medium confidence), while for RCP2.6 sea level rise is projected to be limited to around 1m in 2300 (low confidence). Extreme sea levels and coastal hazards will be exacerbated by projected increases in tropical cyclone intensity and precipitation (high confidence). Projected changes in waves and tides vary locally in whether they amplify or ameliorate these hazards (medium confidence). {Cross-Chapter Box 5 in Chapter 1; Cross-Chapter Box 8 in Chapter 3; 4.1; 4.2; 5.2.2, 6.3.1; Figures SPM.1, SPM.4, SPM.5}

B3.3 The rate of global mean sea level rise is projected to reach 15 mm yr–1 (10–20 mm yr–1, likely range) under RCP8.5 in 2100, and to exceed several centimetres per year in the 22nd century. Under RCP2.6, the rate is projected to reach 4 mm yr-1 (2–6 mm yr–1, likely range) in 2100. Model studies indicate multi-meter rise in sea level by 2300 (2.3–5.4 m for RCP8.5 and 0.6–1.07 m under RCP2.6) (low confidence), indicating the importance of reduced emissions for limiting sea level rise. Processes controlling the timing of future ice-shelf loss and the extent of ice sheet instabilities could increase Antarctica’s contribution to sea level rise to values substantially higher than the likely range on century and longer time-scales (low confidence). Considering the consequences of sea level rise that a  collapse of parts of the Antarctic Ice Sheet entails, this high impact risk merits attention. {Cross-Chapter Box 5 in Chapter 1, Cross-Chapter Box 8 in Chapter 3, 4.1, 4.2.3} B3.4 Global mean sea level rise will cause the frequency of extreme sea level events at most locations
to increase. Local sea levels that historically occurred once per century (historical centennial events) are projected to occur at least annually at most locations by 2100 under all RCP scenarios (high confidence). Many low-lying megacities and small islands (including SIDS) are projected to experience historical centennial events at least annually by 2050 under RCP2.6, RCP4.5 and RCP8.5. The year when the historical centennial event becomes an annual event in the mid-latitudes occurs soonest in RCP8.5, next in RCP4.5 and latest in RCP2.6. The increasing frequency of high water levels can have severe impacts in many locations depending on the level of exposure (high confidence). {4.2.3; 6.3; Figures SPM.4, SPM.5}

B9.1 In the absence of more ambitious adaptation efforts compared to today, and under current trends of increasing exposure and vulnerability of coastal communities, risks, such as erosion and land loss, flooding, salinization, and cascading impacts due to mean sea level rise and extreme events are projected to significantly increase throughout this century under all greenhouse gas emissions scenarios (very high confidence). Under the same assumptions, annual coastal flood damages are projected to increase by 2–3 orders of magnitude by 2100 impaired to today (high confidence). {4.3.3; 4.3.4; Box 6.1; 6.8; SM4.3; Figures SPM.4, SPM.5}

(Bruce M’s Note: 3 orders of magnitude is 1,000 times, or 100,000 percent)

B9.2 High to very high risks are approached for vulnerable communities in coral reef environments, urban atoll islands and low-lying Arctic locations from sea level rise well before the end of this century in case of high emissions scenarios. This entails adaptation limits being reached, which are the points at which an actor’s objectives (or system needs) cannot be secured from intolerable risks through adaptive actions (high confidence). Reaching adaptation limits (e.g., biophysical, geographical, financial, technical, social, political, and institutional) depends on the emissions scenario and context-specific risk tolerance, and is projected to expand to more areas beyond 2100, due to the long-term commitment of sea level rise (medium confidence). Some island nations are likely to become uninhabitable due to climate related ocean and cryosphere change (medium confidence), but habitability thresholds remain extremely difficult to assess. {4.3.4, 4.4.2, 4.4.3, 5.5.2, Cross-Chapter Box 9, SM4.3, SPM C1, Glossary, Figure SPM.5}

B9.3 Globally, a slower rate of climate-related ocean and cryosphere change provides greater
adaptation opportunities (high confidence). While there is high confidence that ambitious adaptation, including governance for transformative change, has the potential to reduce risks in many locations, such benefits can vary between locations. At global scale, coastal protection can reduce flood risk by 2–3 orders of magnitude during the 21st century, but depends on investments on the order of tens to several hundreds of billions of US$ per year (high confidence). While such investments are generally cost efficient for densely populated urban areas, rural and poorer areas may be challenged to afford such investments with relative annual costs for some small island states amounting to several percent of GDP (high confidence). Even with major adaptation efforts, residual risks and associated losses are projected to occur (medium confidence), but context-specific limits to adaptation and residual risks remain difficult to assess. {4.1.3, 4.2.2.4, 4.3.1, 4.3.2, 4.3.4., 4.4.3, 6.9.1, 6.9.2, Cross-Chapter Boxes 1–2 in Chapter 1, SM4.3, Figure SPM.5}