Showing papers in "Nature Climate Change in 2022"

Rapid intensification of the emerging southwestern North American megadrought in 2020–2021

Abstract: A previous reconstruction back to 800 ce indicated that the 2000–2018 soil moisture deficit in southwestern North America was exceeded during one megadrought in the late-1500s. Here, we show that after exceptional drought severity in 2021, ~19% of which is attributable to anthropogenic climate trends, 2000–2021 was the driest 22-yr period since at least 800. This drought will very likely persist through 2022, matching the duration of the late-1500s megadrought. Southwestern North America has been experiencing lower than average precipitation and higher temperatures since 2000. This emerging megadrought, spanning 2000–2021, has been the driest 22-year period since the year 800 and 19% of the drought severity in 2021 can be attributed to climate change.

Over half of known human pathogenic diseases can be aggravated by climate change

Abstract: It is relatively well accepted that climate change can affect human pathogenic diseases; however, the full extent of this risk remains poorly quantified. Here we carried out a systematic search for empirical examples about the impacts of ten climatic hazards sensitive to greenhouse gas (GHG) emissions on each known human pathogenic disease. We found that 58% (that is, 218 out of 375) of infectious diseases confronted by humanity worldwide have been at some point aggravated by climatic hazards; 16% were at times diminished. Empirical cases revealed 1,006 unique pathways in which climatic hazards, via different transmission types, led to pathogenic diseases. The human pathogenic diseases and transmission pathways aggravated by climatic hazards are too numerous for comprehensive societal adaptations, highlighting the urgent need to work at the source of the problem: reducing GHG emissions.

Pronounced loss of Amazon rainforest resilience since the early 2000s

Abstract: Abstract The resilience of the Amazon rainforest to climate and land-use change is crucial for biodiversity, regional climate and the global carbon cycle. Deforestation and climate change, via increasing dry-season length and drought frequency, may already have pushed the Amazon close to a critical threshold of rainforest dieback. Here, we quantify changes of Amazon resilience by applying established indicators (for example, measuring lag-1 autocorrelation) to remotely sensed vegetation data with a focus on vegetation optical depth (1991–2016). We find that more than three-quarters of the Amazon rainforest has been losing resilience since the early 2000s, consistent with the approach to a critical transition. Resilience is being lost faster in regions with less rainfall and in parts of the rainforest that are closer to human activity. We provide direct empirical evidence that the Amazon rainforest is losing resilience, risking dieback with profound implications for biodiversity, carbon storage and climate change at a global scale.

Inequitable patterns of US flood risk in the Anthropocene

Abstract: Abstract Current flood risk mapping, relying on historical observations, fails to account for increasing threat under climate change. Incorporating recent developments in inundation modelling, here we show a 26.4% (24.1–29.1%) increase in US flood risk by 2050 due to climate change alone under RCP4.5. Our national depiction of comprehensive and high-resolution flood risk estimates in the United States indicates current average annual losses of US$32.1 billion (US$30.5–33.8 billion) in 2020’s climate, which are borne disproportionately by poorer communities with a proportionally larger White population. The future increase in risk will disproportionately impact Black communities, while remaining concentrated on the Atlantic and Gulf coasts. Furthermore, projected population change (SSP2) could cause flood risk increases that outweigh the impact of climate change fourfold. These results make clear the need for adaptation to flood and emergent climate risks in the United States, with mitigation required to prevent the acceleration of these risks.

Tropical cyclone climatology change greatly exacerbates US extreme rainfall–surge hazard

Abstract: Abstract Tropical cyclones (TCs) are drivers of extreme rainfall and surge, but the current and future TC rainfall–surge joint hazard has not been well quantified. Using a physics-based approach to simulate TC rainfall and storm tides, we show drastic increases in the joint hazard from historical to projected future (SSP5–8.5) conditions. The frequency of joint extreme events (exceeding both hazards’ historical 100-year levels) may increase by 7–36-fold in the southern US and 30–195-fold in the Northeast by 2100. This increase in joint hazard is induced by sea-level rise and TC climatology change; the relative contribution of TC climatology change is higher than that of sea-level rise for 96% of the coast, largely due to rainfall increases. Increasing storm intensity and decreasing translation speed are the main TC change factors that cause higher rainfall and storm tides and up to 25% increase in their dependence.

Precipitation trends determine future occurrences of compound hot–dry events

Abstract: Abstract Compound hot–dry events—co-occurring hot and dry extremes—frequently cause damages to human and natural systems, often exceeding separate impacts from heatwaves and droughts. Strong increases in the occurrence of these events are projected with warming, but associated uncertainties remain large and poorly understood. Here, using climate model large ensembles, we show that mean precipitation trends exclusively modulate the future occurrence of compound hot–dry events over land. This occurs because local warming will be large enough that future droughts will always coincide with at least moderately hot extremes, even in a 2 °C warmer world. By contrast, precipitation trends are often weak and equivocal in sign, depending on the model, region and internal climate variability. Therefore, constraining regional precipitation trends will also constrain future compound hot–dry events. These results help to assess future frequencies of other compound extremes characterized by strongly different trends in the drivers.

Increased ENSO sea surface temperature variability under four IPCC emission scenarios

Abstract: Abstract Sea surface temperature (SST) variability of El Niño–Southern Oscillation (ENSO) underpins its global impact, and its future change is a long-standing science issue. In its sixth assessment, the IPCC reports no systematic change in ENSO SST variability under any emission scenarios considered. However, comparison between the 20th and 21st century shows a robust increase in century-long ENSO SST variability under four IPCC plausible emission scenarios.

Potential impacts and challenges of border carbon adjustments

Abstract: Harmonized carbon pricing across borders is hard to achieve in the real world as carbon leakage can reduce the cost-effectiveness of unilateral approaches to reduce global emissions. To address this problem, border carbon adjustments (BCAs) would apply the domestic carbon price to emissions embodied in traded goods, which levels the playing field for emissions-intensive and trade-exposed industries. Here, we review the potential environmental and economic impact of border carbon adjustments on leakage reduction, competitiveness restoration, cost-effectiveness, equity and cooperation enhancement. We find that the viability of border carbon adjustment schemes can be substantially reduced with the current legal and practical implementation constraints. Border carbon adjustments are appraised as a measure to address carbon leakage and competitiveness concerns. This Review Article discusses the possible impacts, as well as practical challenges for implementation.

Aligning artificial intelligence with climate change mitigation

Abstract: There is great interest in how the growth of artificial intelligence and machine learning may affect global GHG emissions. However, such emissions impacts remain uncertain, owing in part to the diverse mechanisms through which they occur, posing difficulties for measurement and forecasting. Here we introduce a systematic framework for describing the effects of machine learning (ML) on GHG emissions, encompassing three categories: computing-related impacts, immediate impacts of applying ML and system-level impacts. Using this framework, we identify priorities for impact assessment and scenario analysis, and suggest policy levers for better understanding and shaping the effects of ML on climate change mitigation. The rapid growth of artificial intelligence (AI) is reshaping our society in many ways, and climate change is no exception. This Perspective presents a framework to assess how AI affects GHG emissions and proposes approaches to align the technology with climate change mitigation.

Widespread shift from ecosystem energy to water limitation with climate change

Abstract: Abstract Terrestrial ecosystems are essential for food and water security and CO 2 uptake. Ecosystem function is dependent on the availability of soil moisture, yet it is unclear how climate change will alter soil moisture limitation on vegetation. Here we use an ecosystem index that distinguishes energy and water limitations in Earth system model simulations to show a widespread regime shift from energy to water limitation between 1980 and 2100. This shift is found in both space and time. While this is mainly related to a reduction in energy-limited regions associated with increasing incoming shortwave radiation, the largest shift towards water limitation is found in regions where incoming shortwave radiation increases are accompanied by soil moisture decreases. We therefore demonstrate a widespread regime shift in ecosystem function that is stronger than implied by individual trends in incoming shortwave radiation, soil moisture and terrestrial evaporation, with important implications for future ecosystem services.

Meta-analyses of fifteen determinants of public opinion about climate change taxes and laws

Abstract: Abstract Public acceptance is a precondition for implementing taxes and laws aimed at mitigating climate change. However, it still remains challenging to understand its determinants for the climate community. Here, we use a meta-analytic approach to examine the role of public opinion about climate change taxes and laws. Fifteen variables were examined by synthesizing 89 datasets from 51 articles across 33 countries, with a total sample of 119,465 participants. Among all factors, perceived fairness and effectiveness were the most important determinants. Self-enhancement values and knowledge about climate change showed weak relationships and demographic variables showed only weak or close to zero effects. Our meta-analytic results provide useful insights and have the potential to inform climate change researchers, practitioners and policymakers to better design climate policy instruments.

Climate change experiences raise environmental concerns and promote Green voting

Abstract: Public support is fundamental in scaling up actions to limit global warming. Here, we analyse how the experience of climate extremes influences people’s environmental attitudes and willingness to vote for Green parties in Europe. To this end, we combined high-resolution climatological data with regionally aggregated, harmonized Eurobarometer data (34 countries) and European Parliamentary electoral data (28 countries). Our findings show a significant and sizeable effect of temperature anomalies, heat episodes and dry spells on environmental concern and voting for Green parties. The magnitude of the climate effect differs substantially across European regions. It is stronger in regions with a cooler Continental or temperate Atlantic climate and weaker in regions with a warmer Mediterranean climate. The relationships are moderated by regional income level suggesting that climate change experiences increase public support for climate action but only under favourable economic conditions. The findings have important implications for the current efforts to promote climate action in line with the Paris Agreement. Exposure to extreme weather events could increase environmental concerns and support for Green parties. With high-resolution data across European countries, the authors demonstrate the existence of such effect, then further discuss the heterogeneity and possible mechanisms.

African heritage sites threatened as sea-level rise accelerates

Abstract: Abstract The African coast contains heritage sites of ‘Outstanding Universal Value’ that face increasing risk from anthropogenic climate change. Here, we generated a database of 213 natural and 71 cultural African heritage sites to assess exposure to coastal flooding and erosion under moderate (RCP 4.5) and high (RCP 8.5) greenhouse gas emission scenarios. Currently, 56 sites (20%) are at risk from a 1-in-100-year coastal extreme event, including the iconic ruins of Tipasa (Algeria) and the North Sinai Archaeological Sites Zone (Egypt). By 2050, the number of exposed sites is projected to more than triple, reaching almost 200 sites under high emissions. Emissions mitigation from RCP 8.5 to RCP 4.5 reduces the number of very highly exposed sites by 25%. These findings highlight the urgent need for increased climate change adaptation for heritage sites in Africa, including governance and management approaches, site-specific vulnerability assessments, exposure monitoring, and protection strategies.

Stranded fossil-fuel assets translate to major losses for investors in advanced economies

Abstract: Abstract The distribution of ownership of transition risk associated with stranded fossil-fuel assets remains poorly understood. We calculate that global stranded assets as present value of future lost profits in the upstream oil and gas sector exceed US$1 trillion under plausible changes in expectations about the effects of climate policy. We trace the equity risk ownership from 43,439 oil and gas production assets through a global equity network of 1.8 million companies to their ultimate owners. Most of the market risk falls on private investors, overwhelmingly in OECD countries, including substantial exposure through pension funds and financial markets. The ownership distribution reveals an international net transfer of more than 15% of global stranded asset risk to OECD-based investors. Rich country stakeholders therefore have a major stake in how the transition in oil and gas production is managed, as ongoing supporters of the fossil-fuel economy and potentially exposed owners of stranded assets.

Declining tropical cyclone frequency under global warming

Abstract: Abstract Assessing the role of anthropogenic warming from temporally inhomogeneous historical data in the presence of large natural variability is difficult and has caused conflicting conclusions on detection and attribution of tropical cyclone (TC) trends. Here, using a reconstructed long-term proxy of annual TC numbers together with high-resolution climate model experiments, we show robust declining trends in the annual number of TCs at global and regional scales during the twentieth century. The Twentieth Century Reanalysis (20CR) dataset is used for reconstruction because, compared with other reanalyses, it assimilates only sea-level pressure fields rather than utilize all available observations in the troposphere, making it less sensitive to temporal inhomogeneities in the observations. It can also capture TC signatures from the pre-satellite era reasonably well. The declining trends found are consistent with the twentieth century weakening of the Hadley and Walker circulations, which make conditions for TC formation less favourable.

Emissions rebound from the COVID-19 pandemic

Abstract: Global CO2 emissions in 2021 were only 1% less than the record levels of 2019, driven by increases in power- and industry-related emissions from China and India and a return of the carbon intensity of electricity to pre-pandemic levels. Is this resumed growth in fossil energy, or a final fleeting surge before a long decline?

Limited impacts of carbon tax rebate programmes on public support for carbon pricing

Abstract: Revenue recycling through lump-sum dividends may help mitigate public opposition to carbon taxes, yet evidence from real-world policies is lacking. Here we use survey data from Canada and Switzerland, the only countries with climate rebate programmes, to show low public awareness and substantial underestimation of climate rebate amounts in both countries. Information was obtained using a five-wave panel survey that tracked public attitudes before, during and after implementation of Canada’s 2019 carbon tax and dividend policy and a large-scale survey of Swiss residents. Experimental provision of individualized information about true rebate amounts had modest impacts on public support in Switzerland but potentially deleterious effects on support in Canada, especially among Conservative voters. In both countries, we find that perceptions of climate rebates are structured less by informed assessments of economic interest than by partisan identities. These results suggest limited effects of existing rebate programmes, to date, in reshaping the politics of carbon taxation. Carbon tax rebate programmes have received increasing interest with the potential to raise public support for carbon pricing. However, results of online surveys based on existing real-world policies demonstrate such programmes have had limited political impacts to date.

Ambitious partnership needed for reliable climate prediction

Abstract: Current global climate models struggle to represent precipitation and related extreme events, with serious implications for the physical evidence base to support climate actions. A leap to kilometre-scale models could overcome this shortcoming but requires collaboration on an unprecedented scale.

Biophysical and economic constraints on China’s natural climate solutions

Abstract: Natural climate solutions (NCS) are strategies for climate mitigation in the land sector that increase carbon storage or avoid GHG emissions. Here we estimate China’s historic NCS mitigation at 0.6 (0.5–0.7) PgCO2e yr−1 (95% CI) during 2000–2020 (8% of fossil CO2 emissions in the contemporary period). Through new NCS activities, the future maximum potential for NCS is projected at 0.6 (0.3–1.0) PgCO2e yr−1 (6% of fossil CO2 emissions) during 2020–2030 and 1.0 (0.6–1.4) PgCO2e yr−1 during 2020–2060. Of the future NCS potentials, 26–31%, 62–65% and 90–91% can be achieved at mitigation costs of US$10, US$50 and US$100 (MgCO2e)−1, respectively. Thus, NCS can contribute substantially to China’s Nationally Determined Contributions over the next 10 to 40 years but require a national strategy to reach climate goals and ensure co-benefits for people and nature.

Enhanced risk of concurrent regional droughts with increased ENSO variability and warming

Abstract: Spatially compounding extremes pose substantial threats to globally interconnected socio-economic systems. Here we use multiple large ensemble simulations of the high-emissions scenario to show increased risk of compound droughts during the boreal summer over ten global regions. Relative to the late twentieth century, the probability of compound droughts increases by ~40% and ~60% by the middle and late twenty-first century, respectively, with a disproportionate increase in risk across North America and the Amazon. These changes contribute to an approximately ninefold increase in agricultural area and population exposure to severe compound droughts with continued fossil-fuel dependence. ENSO is the predominant large-scale driver of compound droughts with 68% of historical events occurring during El Niño or La Niña conditions. With ENSO teleconnections remaining largely stationary in the future, a ~22% increase in frequency of ENSO events combined with projected warming drives the elevated risk of compound droughts. The co-occurrence of drought across different regions will have far-reaching effects on global agriculture and food supply. Model projections show an increased likelihood of these compound droughts under a high-emissions scenario, with a ninefold increase of farm land and population exposure.

Soil quality both increases crop production and improves resilience to climate change

Abstract: Interactions between soil quality and climate change may influence the capacity of croplands to produce sufficient food. Here, we address this issue by using a new dataset of soil, climate and associated yield observations for 12,115 site-years representing 90% of total cereal production in China. Across crops and environmental conditions, we show that high-quality soils reduced the sensitivity of crop yield to climate variability leading to both higher mean crop yield (10.3 ± 6.7%) and higher yield stability (decreasing variability by 15.6 ± 14.4%). High-quality soils improve the outcome for yields under climate change by 1.7% (0.5–4.0%), compared to low-quality soils. Climate-driven yield change could result in reductions of national cereal production of 11.4 Mt annually under representative concentration pathway RCP 8.5 by 2080–2099. While this production reduction was exacerbated by 14% due to soil degradation, it can be reduced by 21% through soil improvement. This study emphasizes the vital role of soil quality in agriculture under climate change. Food demand is increasing, while climate change is impacting the magnitude and stability of crop yields. High-quality soils are able to buffer the negative impacts of climate change and lead to smaller yield reduction and higher yield stability, indicating a potential adaptation strategy.

Imminent loss of climate space for permafrost peatlands in Europe and Western Siberia

Abstract: Human-induced climate warming by 2100 is expected to thaw large expanses of northern permafrost peatlands. However, the spatio-temporal dynamics of permafrost peatland thaw remain uncertain due to complex permafrost–climate interactions, the insulating properties of peat soils and variation in model projections of future climate. Here we show that permafrost peatlands in Europe and Western Siberia will soon surpass a climatic tipping point under scenarios of moderate-to-high warming (Shared Socioeconomic Pathway (SSP) 2-4.5, SSP3-7.0 and SSP5-8.5). The total peatland area affected under these scenarios contains 37.0–39.5 Gt carbon (equivalent to twice the amount of carbon stored in European forests). Our bioclimatic models indicate that all of Fennoscandia will become climatically unsuitable for peatland permafrost by 2040. Strong action to reduce emissions (SSP1-2.6) by the 2090s could retain suitable climates for permafrost peatlands storing 13.9 Gt carbon in northernmost Western Siberia, indicating that socio-economic policies will determine the rate and extent of permafrost peatland thaw. Permafrost peatlands are thawing, yet the timing and spatial dynamics of thaw are not well constrained. Under moderate and high warming scenarios, permafrost peatlands in Europe and Western Siberia will cross a tipping point where the climate becomes unsuitable, putting their carbon stores at risk.

South Asian agriculture increasingly dependent on meltwater and groundwater

Abstract: Irrigated agriculture in South Asia depends on meltwater, monsoon rains and groundwater. Climate change alters the hydrology and causes shifts in the timing, composition and magnitude of these sources of water supply. Simultaneously, socio-economic growth increases water demand. Here we use a high-resolution cryosphere–hydrology–crop model forced with an ensemble of climate and socio-economic projections to assess how the sources of irrigation water supply may shift during the twenty-first century. We find increases in the importance of meltwater and groundwater for irrigated agriculture. An earlier melt peak increases meltwater withdrawal at the onset of the cropping season in May and June in the Indus, whereas increasing peak irrigation water demand during July and August aggravates non-renewable groundwater pumping in the Indus and Ganges despite runoff increases. Increasing inter-annual variability in rainfall runoff increases the need for meltwater and groundwater to complement rainfall runoff during future dry years. South Asian agriculture depends on water from rains, meltwater and groundwater, but climate change impacts the timing of these water sources’ availability. Projections indicate that meltwater and groundwater will become more important and will need to offset reduced rainfall during drier years.

Ageing society in developed countries challenges carbon mitigation

Abstract: Populations in developed countries are ageing. However, the impact of senior citizens’ consumption on global carbon mitigation is poorly understood. Here we find that senior citizens have played a leading role in driving up GHG emissions in the past decade and are on the way to becoming the largest contributor. Considering the greenhouse gas footprint of household consumption across age groups in 32 developed countries, the senior contribution to national total consumption-based emissions increased from 25.2% to 32.7% between 2005 and 2015. Seniors in the United States and Australia have the highest per capita footprint, twice the Western average. The trend is mainly due to changes in expenditure patterns of seniors. The increasing carbon footprint of senior citizens will probably drive domestic production yet have limited effects on international carbon leakage. The demographic change poses more challenges in local mitigation and calls for deeper public mitigation efforts. A large proportion of the population in developed countries will be of senior age in the years ahead. The carbon emissions of this group comprised an increasing share of the total emissions in developed countries in the past decade, with high expenditure on carbon-intensive products, and this trend will continue in the future.

Tropical forest restoration under future climate change

Abstract: Abstract One of the most promising ways to rapidly remove CO 2 from the atmosphere is through the restoration of tropical forests. Ongoing and future climate change may, however, threaten the permanence of carbon stored through restoration. Excessive heat, drought or increased disturbances such as wildfire could all negatively impact the integrity of restored carbon. To investigate these risks to tropical forest restoration, we performed 221 simulations with a dynamic global vegetation model (LPJ-LMfire) driven by a range of future climate scenarios and ecophysiological responses to CO 2 concentrations. We show that carbon in restored tropical forests is largely preserved under the entire range of potential future climates, regardless of assumptions we make about the potential for CO 2 fertilization of photosynthesis. Restoring even half of the potential area can account for 56–69% of the carbon storage, depending on whether areas are selected for low cost or high carbon gain.