Atmospheric Greenhouse Gas Concentrations Research Articles

The Atmospheric Concentration of Common Greenhouse Gases in the Pulpwood Plantation in Riau Province, Indonesia

Pulp and paper wood plantations are one of the substantial forestry estates in Indonesia that are usually integrated with a pulp and paper mill industry. The atmospheric condition of glasshouse gases that keep increasing primarily due to anthropogenic activities represent critical issues on human health and affect forest productivity. Therefore this study measured the atmospheric concentration of common glasshouse gases in the pulpwood plantation integrated with a pulp mill in Riau Province. Overly high concentration of some glasshouse gases in the atmosphere may cause issues and at an extreme level, may lead to the occurrence of acid rain that could affect forest health and productivity. This study employed the Ogawa Passive Sampler Method to determine the air concentration of common glasshouse gases, i.e., [SOx], [NOx], [NO2], and [O3] in different rotations and stand ages of Acacia crassicarpa and Eucalyptus pellita stands. The results showed that species, rotation age, and stand age affect the concentration of gaseous N in the plantations. The concentrations of [NOx] and [NO2] gases were higher in the old rotation than in the young rotation of A. crassicarpa stands. Those concentrations were also relatively higher in peat soil sites than in non-peat soil sites.

The Potential Role of Biodiversity Conservation in Climate Change Mitigation: A Review

This review paper aims to compile relevant information on the potential of biodiversity conservation in climate change mitigation. The global climate change is the result of the concentration of greenhouse gases: dominantly of carbon dioxide, methane and nitrous oxide emitted into the atmosphere. The root causes for these emissions are the natural phenomenon and human-induced activity in which high pressure poses on the environment from human-driven. Evidence from previous study indicates that biodiversity components are widely influenced under climate change and at the same time, the conservation of biodiversity potentially mitigates the effect of the global climate change. As a result, there is a beneficial and adverse effect type of co-existence of two ecological components (i.e. the living and non-living) in this interaction. Biodiversity has the potential to mitigate climate change as they reduce and stabilize atmospheric greenhouse gas concentrations. Thus, in such mitigation process, Forestry and Agricultural practices contribute a lion's share based on their potential to absorb and store carbon from the atmosphere, reduce deforestation and biodiversity degradation, and provide bio-energy products that substitute for fossil energy. Therefore, the global community should be needed to done in collaboration on biodiversity conservation to improve climate change mitigation potential of biological diversity.

Strengthening the Role of Forests in Climate Change Mitigation through the European Union Forest Law Enforcement, Governance and Trade Action Plan

Forests influence climate change by either increasing or decreasing the atmospheric concentration of greenhouse gases. When unsustainably managed, forests can release more greenhouse gases than they can absorb, intensifying their atmospheric concentration with adverse climate and human health outcomes. Several frameworks and institutional arrangements have been adopted globally to help strengthen political commitment and actions to promote the sustainable management of forests and enhance forests’ contribution to climate change mitigation. Nevertheless, the destruction of tropical forests is accelerating at an alarming rate, making it an uphill battle to stop forest sector carbon emissions, limit the global average temperature rise to well below 2°C, and build a sustainable and climate-resilient future for all. The continuous release of forest-related emissions indicates that humanity has fallen short of meeting global forest and climate-related goals and, hence, reiterates the need to develop and apply additional tools to support international cooperation on mitigating forest carbon emissions. Considering deforestation’s challenge for voluntary frameworks such as the UN Forest Instrument and REDD+, opportunities/actions beyond non-legally binding agreements and principles must be harnessed promptly. Trade-related measures, such as the Forest Law Enforcement, Governance and Trade Action Plan, are relevant in addressing deforestation. Arguably, the Forest Law Enforcement, Governance and Trade Action Plan provides the most appropriate framework for future regional/global forest law reform.

Microalgae potential in the capture of CO2 emission

In a perspective projected to reduce the atmospheric concentration of greenhouse gases, in which carbon dioxide is the master, the use of microalgae is an effective and decisive response. The review describes the bio circularity of the process of abatement of carbon dioxide through biofixation in algal biomass, highlighting the potential of its reuse in the production of high value-added products.

Dynamic Life Cycle Assessment of Energy Technologies under Different Greenhouse Gas Concentration Pathways.

Global warming potential (GWP) has been widely used in the life cycle assessment (LCA) to quantify the climate impacts of energy technologies. Most LCAs are static analyses without considering the dynamics of greenhouse gas (GHG) emissions and changes in background GHG concentrations. This study presents a dynamic approach to analyze the life-cycle GWP of energy technologies in different timeframes and representative GHG concentration pathways. Results show that higher atmospheric GHG concentrations lead to higher life-cycle GWP for long-term analysis. The impacts of background GHG concentrations are more significant for technologies with large operational emissions or CH4 emissions than technologies with low operational emissions. The case study for the U.S. electricity sector in 2020-2050 shows the impacts of background GHG concentrations and different LCA methods on estimating national climate impacts of different energy technology scenarios. Based on the results, it is recommended for future LCAs to incorporate temporal effects of GHG emissions when (1) the technology has large operational GHG emissions or CH4 emissions; (2) the analysis time frame is longer than 50 years; (3) when LCA results are used for policymaking or technology comparisons for mitigating climate change.

Reduced effective radiative forcing from cloud–aerosol interactions (ERF<sub>aci</sub>) with improved treatment of early aerosol growth in an Earth system model

Abstract. Historically, aerosols of anthropogenic origin have offset some of the warming from increased atmospheric greenhouse gas concentrations. The strength of this negative aerosol forcing, however, is highly uncertain – especially the part originating from cloud–aerosol interactions. An important part of this uncertainty originates from our lack of knowledge about pre-industrial aerosols and how many of these would have acted as cloud condensation nuclei (CCN). In order to simulate CCN concentrations in models, we must adequately model secondary aerosols, including new particle formation (NPF) and early growth, which contributes a large part of atmospheric CCN. In this study, we investigate the effective radiative forcing (ERF) from cloud–aerosol interactions (ERFaci) with an improved treatment of early particle growth, as presented in Blichner et al. (2021). We compare the improved scheme to the default scheme, OsloAero, which are both embedded in the atmospheric component of the Norwegian Earth System Model v2 (NorESM2). The improved scheme, OsloAeroSec, includes a sectional scheme that treats the growth of particles from 5–39.6 nm in diameter, which thereafter inputs the particles to the smallest mode in the pre-existing modal aerosol scheme. The default scheme parameterizes the growth of particles from nucleation up to the smallest mode, a process that can take several hours. The explicit treatment of early growth in OsloAeroSec, on the other hand, captures the changes in atmospheric conditions during this growth time in terms of air mass mixing, transport, and condensation and coagulation. We find that the ERFaci with the sectional scheme is −1.16 W m−2, which is 0.13 W m−2 weaker compared to the default scheme. This reduction originates from OsloAeroSec producing more particles than the default scheme in pristine, low-aerosol-concentration areas and fewer NPF particles in high-aerosol areas. We find, perhaps surprisingly, that NPF inhibits cloud droplet activation in polluted and/or high-aerosol-concentration regions because the NPF particles increase the condensation sink and reduce the growth of the larger particles which may otherwise activate. This means that in these high-aerosol regions, the model with the lowest NPF – OsloAeroSec – will have the highest cloud droplet activation and thus more reflective clouds. In pristine and/or low-aerosol regions, however, NPF enhances cloud droplet activation because the NPF particles themselves tend to activate. Lastly, we find that sulfate emissions in the present-day simulations increase the hygroscopicity of secondary aerosols compared to pre-industrial simulations. This makes NPF particles more relevant for cloud droplet activation in the present day than the pre-industrial atmosphere because increased hygroscopicity means they can activate at smaller sizes.

Impact of climate change on hydropower potential of the Lagdo dam, Benue River Basin, Northern Cameroon

Abstract. Nowadays, special attention is paid to hydroelectric production because it is an efficient, reliable, and renewable source of energy, especially in developing countries like Cameroon, where hydropower potential is the main source of electricity production. It also represents a useful tool to reduce the atmospheric greenhouse gas concentrations caused by human activities. However, it is the most sensitive industry to global warming, mainly because climate change will directly affect the quality, quantity of water resources (streamflow and runoff), which are the important drivers of hydropower potential. This study examined the response of hydropower potential to climate change on the Lagdo dam located in the Benue River Basin, Northern Cameroon. Hydropower potential was computed based on streamflow simulated using HBV-Light hydrological model with dynamically downscaled temperature and precipitation from the regional climate model REMO. These data were obtained using the boundary conditions of two general circulation models (GCMs): the Europe-wide Consortium Earth System Model (EC-Earth) and the Max Planck Institute-Earth System Model (MPI-ESM) under three Representative Concentrations Pathways (RCP2.6, RCP4.5 and RCP8.5). The results suggest that, the combination of decreased precipitation and streamflow, increased PET will negatively impact the hydropower potential in the Lagdo dam under climate change scenarios, models and future periods.

Sounding Out the Carbon: The Potential of Acoustic Backscatter Data to Yield Improved Spatial Predictions of Organic Carbon in Marine Sediments

Marine sediments hold vast stores of organic carbon (OC). Techniques to spatially map sedimentary OC must develop to form the basis of seabed management tools that consider carbon-rich sediments. While the natural burial of carbon (C) provides a climate regulation service, the disturbance of buried C could present a significant positive feedback mechanism to atmospheric greenhouse gas concentrations. We present a regional Scottish case study that explores the suitability of integrating archived seafloor acoustic data (i.e., multibeam echosounder bathymetry and backscatter) with physical samples toward improved spatial mapping of surface OC in a dynamic coastal environment. Acoustic backscatter is a proxy for seabed sediments and can be collected over extensive areas at high resolutions. Sediment type is also an important predictor of OC. We test the potential of backscatter as a proxy for OC which may prove useful in the absence of exhaustive sediment data. Overall, although statistically significant, correlations between the variables OC, sediment type, and backscatter are relatively weak, likely reflecting a combination of limited and asynchronous data, sediment mobility over time, and complex environmental processing of OC in shelf sediments. We estimate linear mixed models to predict OC using backscatter and Folk sediment type as covariates. Our results show that incorporating backscatter in the model improves the precision of OC predictions by 14%. Backscatter discriminates between coarse and fine sediments, and therefore low and high OC regimes; however, was not able to discriminate amongst finer sediments. Although sediment type is a stronger predictor of OC, these data are available at a much lower spatial resolution and do not account for fine-scale variability. The resulting maps display varying spatial distributions of OC reflecting the different scales of the predictor variables, demonstrating a need for further methodological development. Backscatter shows considerable promise as a high-resolution predictor variable to improve the precision of surface OC maps, or to reduce the number of OC measurements required to achieve a specified precision. Applications of such maps have potential in improved C-stock estimates and the design of conservation and management strategies that consider marine sediments as valuable C stores.

Last millennium climate changes over the Antarctic Peninsula and southern Patagonia in CESM-LME simulations: Differences between Medieval Climate Anomaly and present-day temperatures

This paper describes differences between Medieval Climate Anomaly (MCA) and present-day temperatures in the area composed of the Antarctic Peninsula, southern Patagonia, and the surrounding southern oceans. The investigation is conducted with the simulation results from the Community Earth System Model Last Millennium Ensemble (CESM-LME) considering the impact of each natural (volcanic activity and solar variability) and anthropogenic (greenhouse gas, ozone-aerosols and land use/land cover) individual forcing relative to the full forced simulations. Model results show generalized warming during the MCA in the study area. However, the simulated MCA temperatures are significantly colder than present-day mean values due to the influence of increased atmospheric greenhouse gas concentrations since the beginning of the modern Industrial Era in the ∼1850s. In fact, model runs in which only natural forcings were applied show that, in the absence of greenhouse gas forcing, present-day temperatures in the Antarctic Peninsula and southern Patagonia would be lower than or similar to those during the MCA. The study demonstrates the value of paleoclimate proxy–model comparisons but also highlights the limitations of current available proxy information to perform that integration in the study area.

The magnitude, direction, and tempo of forest change in Greater Yellowstone in a warmer world with more fire

AbstractAs temperatures continue rising, the direction, magnitude, and tempo of change in disturbance‐prone forests remain unresolved. Even forests long resilient to stand‐replacing fire face uncertain futures, and efforts to project changes in forest structure and composition are sorely needed to anticipate future forest trajectories. We simulated fire (incorporating fuels feedbacks) and forest dynamics on five landscapes spanning the Greater Yellowstone Ecosystem (GYE) to ask the following questions: (1) How and where are forest landscapes likely to change with 21st‐century warming and fire activity? (2) Are future forest changes gradual or abrupt, and do forest attributes change synchronously or sequentially? (3) Can forest declines be averted by mid‐21st‐century stabilization of atmospheric greenhouse gas (GHG) concentrations? We used the spatially explicit individual‐based forest model iLand to track multiple attributes (forest extent, stand age, tree density, basal area, aboveground carbon stocks, dominant forest types, species occupancy) through 2100 for six climate scenarios. Hot‐dry climate scenarios led to more fire, but stand‐replacing fire peaked in mid‐century and then declined even as annual area burned continued to rise. Where forest cover persisted, previously dense forests were converted to sparse young woodlands. Increased aridity and fire drove a ratchet of successive abrupt declines (i.e., multiple annual landscape‐level changes ≥20%) in tree density, basal area, and extent of older (>150 yr) forests, whereas declines in carbon stocks and mean stand age were always gradual. Forest changes were asynchronous across landscapes, but declines in stand structure always preceded reductions in forest extent and carbon stocks. Forest decline was most likely in less topographically complex landscapes dominated by fire‐sensitive tree species (Picea engelmannii, Abies lasiocarpa, Pinus contorta var. latifolia) and where fire resisters (Pseudotsuga menziesii var. glauca) were not already prevalent. If current GHG emissions continue unabated (RCP 8.5) and aridity increases, a suite of forest changes would transform the GYE, with cascading effects on biodiversity and myriad ecosystem services. However, stabilizing GHG concentrations by mid‐century (RCP 4.5) would slow the ratchet, moderating fire activity and dampening the magnitude and rate of forest change. Monitoring changes in forest structure may serve as an operational early warning indicator of impending forest decline.

Dengue transmission risk in a changing climate: Bangladesh is likely to experience a longer dengue fever season in the future

Our changing climate is already affecting the transmission of dengue fever, the fastest growing vector-borne viral disease in the world. This issue presents a significant public health concern for some nations, such as Bangladesh, which already experience regular seasonal outbreaks of dengue fever under present day conditions. To provide guidance for proactive public health planning to potentially mitigate the severity of future outbreaks, we explored the impact of climate change on dengue infections by calculating the change in vectorial capacity (VC) of Aedes aegypti mosquitoes at a seasonal level for all regions in Bangladesh under two scenarios for future atmospheric greenhouse gas concentrations. For each of the four climate models used, and for both scenarios, our analysis revealed that the annual VC remains at a level that would enable potential dengue epidemic transmission in all regions in Bangladesh. We found a slight decline in VC in half of the regions examined during the last two decades of the 21st century for the lower-concentration scenario, with a pronounced decline in VC in all geographic regions beginning in 2060 for the higher-concentration scenario. The likely reason is that in many regions, warming will lead to sub-optimal mosquito breeding temperatures. However, seasonal differences in VC will dissipate as the climate warms, to the point that there is almost no observable seasonality for the higher-concentration scenario during the last two decades of this century. This finding suggests the dengue transmission season could eventually extend to all-year-round transmission, with outbreaks occurring at any time. Consequently, disease surveillance and control activities would need to be geographically and temporally adapted to mitigate dengue epidemic risk in response to climate change.

The Emergence and Transient Nature of Arctic Amplification in Coupled Climate Models

Under rising atmospheric greenhouse gas concentrations, the Arctic exhibits amplified warming relative to the globe. This Arctic amplification is a defining feature of global warming. However, the Arctic is also home to large internal variability, which can make the detection of a forced climate response difficult. Here we use results from seven model large ensembles, which have different rates of Arctic warming and sea ice loss, to assess the time of emergence of anthropogenically-forced Arctic amplification. We find that this time of emergence occurs at the turn of the century in all models, ranging across the models by a decade from 1994–2005. We also assess transient changes in this amplified signal across the 21st century and beyond. Over the 21st century, the projections indicate that the maximum Arctic warming will transition from fall to winter due to sea ice reductions that extend further into the fall. Additionally, the magnitude of the annual amplification signal declines over the 21st century associated in part with a weakening albedo feedback strength. In a simulation that extends to the 23rd century, we find that as sea ice cover is completely lost, there is little further reduction in the surface albedo and Arctic amplification saturates at a level that is reduced from its 21st century value.

Near-surface atmospheric concentrations of greenhouse gases (CO2 and CH4) in Florence urban area: Inferring emitting sources through carbon isotopic analysis

From February to April 2019, near-surface CO2 and CH4 concentrations and carbon isotopic compositions (δ13C-CO2 and δ13C-CH4) were monitored at four stations belonging to the local air quality surveillance network of Florence (central Italy), representing typical zones of suburban background (SB), urban traffic (UT) and urban background (UB). The GHGs (greenhouse gases) concentrations showed a high spatial variability likely related to variable contributions from distinct emitting sources in the urban landscape. The δ13C-CO2 and δ13C-CH4 values suggested that domestic heating is the dominant GHGs emitting source at the UB station. Conversely, traffic-related CO2 emissions (about 74%) largely overwhelmed those from natural gas combustion at the UT stations, where vehicular exhaust emissions also affected atmospheric CH4 levels. The SB and UB stations registered the presence of multiple CH4 sources, which included both leakage from underground pipeline network for natural gas supply and biogenic emissions from urban waterways. These results offer a pivotal background framework to improve the performance of GHGs reduction policies and refine the spatiotemporal resolution of bottom-up estimations of urban GHG emissions.

Note for COP26 on Marine Cloud Brightening

Present policies of most Governments, with a few predictable exceptions, concentrate on the desperate need to get to zero carbon emissions as soon as possible. This is a necessary but not sufficient objective. There is strong evidence from the Keeling curve in figure 1, about the difficulty (Figure 1). Figure 1: But if we could reduce, carbon emissions to zero the concentration of atmospheric greenhouse gases will be what we have now plus what we will be emitting between now and the zero-emission date minus the amount taken up by the oceans. This means that typhoons, floods, droughts, bushfires, sea-level rise, Arctic ice loss and damage to coral will all be worse, perhaps much worse than now. If you think that present conditions are not acceptable you have to conclude that zero is not low enough. As well as reducing emissions we will HAVE TO remove greenhouse gases, probably with help from phytoplankton, and also do direct cooling a soon as we can and hopefully ramp it down as emissions reduce [1].

The First Global Carbon Dioxide Flux Map Derived from TanSat Measurements

Space-borne measurements of atmospheric greenhouse gas concentrations provide global observation constraints for top-down estimates of surface carbon flux. Here, the first estimates of the global distribution of carbon surface fluxes inferred from dry-air CO2 column (XCO2) measurements by the Chinese Global Carbon Dioxide Monitoring Scientific Experimental Satellite (TanSat) are presented. An ensemble transform Kalman filter (ETKF) data assimilation system coupled with the GEOS-Chem global chemistry transport model is used to optimally fit model simulations with the TanSat XCO2 observations, which were retrieved using the Institute of Atmospheric Physics Carbon dioxide retrieval Algorithm for Satellite remote sensing (IAPCAS). High posterior error reduction (30%–50%) compared with a priori fluxes indicates that assimilating satellite XCO2 measurements provides highly effective constraints on global carbon flux estimation. Their impacts are also highlighted by significant spatiotemporal shifts in flux patterns over regions critical to the global carbon budget, such as tropical South America and China. An integrated global land carbon net flux of 6.71 ± 0.76 Gt C yr−1 over 12 months (May 2017–April 2018) is estimated from the TanSat XCO2 data, which is generally consistent with other inversions based on satellite data, such as the JAXA GOSAT and NASA OCO-2 XCO2 retrievals. However, discrepancies were found in some regional flux estimates, particularly over the Southern Hemisphere, where there may still be uncorrected bias between satellite measurements due to the lack of independent reference observations. The results of this study provide the groundwork for further studies using current or future TanSat XCO2 data together with other surface-based and space-borne measurements to quantify biosphere-atmosphere carbon exchange.

Local summer insolation and greenhouse gas forcing drove warming and glacier retreat in New Zealand during the Holocene

Geological climate archives from the Holocene Epoch provide baseline information concerning natural climate variability. Temperate mountain glacier extent is sensitive to summer air temperature, thus geological records of past glacier length changes are a useful proxy for this climatic variable. Here we present a new cosmogenic 10Be chronology of glacier length changes at Dart Glacier in the Southern Alps, New Zealand. Prominent moraines deposited 321 ± 44 yr ago (n = 11) and 7.8 ± 0.3 ka (n = 5) show glaciers during the Little Ice Age were less extensive than during the early Holocene. This pattern of net Holocene glacier retreat is consistent with emerging data from other catchments in New Zealand and across the southern mid-latitudes. Using the physical framework of a transient global climate model simulation, we suggest that cool summers in the early Holocene were promoted by the local summer insolation minimum, together with low atmospheric greenhouse gas concentrations, causing an early Holocene austral glacial maximum. An insolation-driven reduction in seasonality at southern mid-latitudes may reconcile differences between early Holocene temperature reconstructions where climate proxies have different seasonal sensitivities. We suggest that rising greenhouse gas concentrations after 7 ka caused regional-scale glacier retreat and appear to be the dominant driver of multi-millennial summer temperature trends in the southern mid-latitudes during the present interglacial.

Monitoring Greenhouse Gases from Space

The increase in atmospheric greenhouse gas concentrations of CO2 and CH4, due to human activities, is the main driver of the observed increase in surface temperature by more than 1 °C since the pre-industrial era. At the 2015 United Nations Climate Change Conference held in Paris, most nations agreed to reduce greenhouse gas emissions to limit the increase in global surface temperature to 1.5 °C. Satellite remote sensing of CO2 and CH4 is now well established thanks to missions such as NASA’s OCO-2 and the Japanese GOSAT missions, which have allowed us to build a long-term record of atmospheric GHG concentrations from space. They also give us a first glimpse into CO2 and CH4 enhancements related to anthropogenic emission, which helps to pave the way towards the future missions aimed at a Monitoring & Verification Support (MVS) capacity for the global stock take of the Paris agreement. China plays an important role for the global carbon budget as the largest source of anthropogenic carbon emissions but also as a region of increased carbon sequestration as a result of several reforestation projects. Over the last 10 years, a series of projects on mitigation of carbon emission has been started in China, including the development of the first Chinese greenhouse gas monitoring satellite mission, TanSat, which was successfully launched on 22 December 2016. Here, we summarise the results of a collaborative project between European and Chinese teams under the framework of the Dragon-4 programme of ESA and the Ministry of Science and Technology (MOST) to characterize and evaluate the datasets from the TanSat mission by retrieval intercomparisons and ground-based validation and to apply model comparisons and surface flux inversion methods to TanSat and other CO2 missions, with a focus on China.

Warming climate forcing impact from a sub-arctic peatland as a result of late Holocene permafrost aggradation and initiation of bare peat surfaces

Effects of permafrost aggradation on greenhouse gas (GHG) dynamics and climate forcing have not been previously quantified. Here, we reconstruct changes in GHG balances over the late Holocene for a sub-arctic peatland by applying palaeoecological data combined with measured GHG flux data, focusing on the impact of permafrost aggradation in particular. Our data suggest that permafrost initiation around 3000 years ago resulted in GHG emissions, thereby slightly weakening the general long-term peatland cooling impact. As a novel discovery, based on our chronological data of bare peat surfaces, we found that current sporadic bare peat surfaces in subarctic regions are probably remnants of more extensive bare peat areas formed by permafrost initiation. Paradoxically, our data suggest that permafrost initiation triggered by the late Holocene cooling climate generated a positive radiative forcing and a short-term climate warming feedback, mitigating the general insolation-driven late Holocene summer cooling trend. Our work with historical data demonstrates the importance of permafrost peatland dynamics for atmospheric GHG concentrations, both in the past and future. It suggests that, while thawing permafrost is likely to initially trigger a change towards wetter conditions and consequent increase in CH4 forcing, eventually the accelerated C uptake capacity under warmer climate may overcome the thaw effect when a new hydrological balance becomes established.

Overshooting tippingpoint thresholds in a changing climate.

Palaeorecords suggest that the climate system has tipping points, where small changes in forcing cause substantial and irreversible alteration to Earth system components called tipping elements. As atmospheric greenhouse gas concentrations continue to rise as a result of fossil fuel burning, human activity could also trigger tipping, and the impacts would be difficult to adapt to. Previous studies report low global warming thresholds above pre-industrial conditions for key tipping elements such as ice-sheet melt. If so, high contemporary rates of warming imply that exceeding these thresholds is almost inevitable, which is widely assumed to mean that we are now committed to suffering these tipping events. Here we show that this assumption may be flawed, especially for slow-onset tipping elements (such as the collapse of the Atlantic Meridional Overturning Circulation) in our rapidly changing climate. Recently developed theory indicates that a threshold may be temporarily exceeded without prompting a change of system state, if the overshoot time is short compared to the effective timescale of the tipping element. To demonstrate this, we consider transparently simple models of tipping elements with prescribed thresholds, driven by global warming trajectories that peak before returning to stabilize at a global warming level of 1.5 degrees Celsius above the pre-industrial level. These results highlight the importance of accounting for timescales when assessing risks associated with overshooting tippingpoint thresholds.

Historical and future global burned area with changing climate and human demography

Summary Wildfires influence terrestrial carbon cycling and represent a safety risk, and yet a process-based understanding of their frequency and spatial distributions remains elusive. We combine satellite-based observations with an enhanced dynamic global vegetation model to make regionally resolved global assessments of burned area (BA) responses to changing climate, derived from 34 Earth system models and human demographics for 1860–2100. Limited by climate and socioeconomics, recent BA has decreased, especially in central South America and mesic African savannas. However, future simulations predict increasing BA due to changing climate, rapid population density growth, and urbanization. BA increases are especially notable at high latitudes, due to accelerated warming, and over the tropics and subtropics, due to drying and human ignitions. Conversely, rapid urbanization also limits BA via enhanced fire suppression in the immediate vicinity of settlements, offsetting the potential for dramatic future increases, depending on warming extent. Our analysis provides further insight into regional and global BA trends, highlighting the importance of including human demographic change in models for wildfire under changing climate.