Home People & Planet The future of the planet is grim and we must act now

The future of the planet is grim and we must act now

The recent UN IPCC report is a clarion call for immediate action
A placard from the global climate change protest demonstration in Bavaria, Germany in 2019

Climate change is a serious threat. It is a crisis that alarmingly still receives more lip service than actual action. The current state of climate change—and its consequent effects—is perilous.   

The recently released UN IPCC (United Nations Intergovernmental Panel on Climate Change) Working Group 1 report “is a code red for humanity,” says UN Secretary General António Guterres. He further adds that “greenhouse gas emissions from fossil fuel burning and deforestation are choking our planet and putting billions of people at immediate risk. Global heating is affecting every region on Earth, with many of the changes becoming irreversible.”

Unprecedented warming

New climate model simulations; analyses of data from paleoclimate archives; and peer-reviewed studies point to a clear trend of increased human influence in the warming of the atmosphere, ocean and land. Since 1970, global surface temperature has increased faster than in any other 50-year period over the last 2,000 years.

Greenhouse gas (GHGs) emissions have increased since 1750 – a leading contributor to global warming. Meanwhile, there has been a cooling influence—although not an environment friendly ally—due to usage of aerosols. Each of the past four decades were incrementally warmer than any earlier period since 1850.

Exhibit 1: History of global temperature change and causes of recent warming

Panel a): Changes in global surface temperature reconstructed from paleoclimate archives (solid grey line, 1–2000) and from direct observations (solid black line, 1850–2020), both relative to 1850–1900 and decadally averaged. The vertical bar on the left shows the estimated temperature (very likely range) during the warmest multi-century period in at least the last 100,000 years, which occurred around 6500 years ago during the current interglacial period (Holocene). The Last Interglacial, around 125,000 years ago, is the next most recent candidate for a period of higher temperature. These past warm periods were caused by slow (multi-millennial) orbital variations. The grey shading with white diagonal lines shows the very likely ranges for the temperature reconstructions. Panel b): Changes in global surface temperature over the past 170 years (black line) relative to 1850–1900 and annually averaged, compared to CMIP6 climate model simulations (see Box SPM.1) of the temperature response to both human and natural drivers (brown), and to only natural drivers (solar and volcanic activity, green). Solid coloured lines show the multi-model average, and coloured shades show the very likely range of simulations.

The report highlights that human activity is the primary contributor to receding glaciers globally since the 1990s, and the decrease in Arctic Sea ice, and its thickness levels, between 1979-1988 and 2010-2019. The Arctic Sea’s ice expanse, in 2020, was at its least in the past 1,000 years. Such massive reductions in glacier and ice sheets sound an ominous warning – that global mean sea levels have also shot up drastically. It increased by 0.20 m between 1901 and 2018.

Increased human influence led to rise in CO2 emissions resulting in increased acidification and heating of the ocean surface. In 2019, CO2 concentration levels were higher than at any time in at least 2 million years. Likewise, methane and nitrogen oxide levels were at their highest in 80,000 years. Compounding the ill effects are declining oxygen levels in many oceanic regions since the mid-20th century. This has led to migration trends being observed in marine organisms over the past two decades.

Exhibit 2: Assessed contributions to observed warming in 2010–2019 relative to 1850–1900

Panel a): Observed global warming (increase in global surface temperature) and its very likely range {3.3.1, Cross-Chapter Box 2.3}. Panel b): Evidence from attribution studies, which synthesize information from climate models and observations. The panel shows temperature change attributed to total human influence, changes in well-mixed greenhouse gas concentrations, other human drivers due to aerosols, ozone and land-use change (land-use reflectance), solar and volcanic drivers, and internal climate variability. Whiskers show likely ranges {3.3.1}. Panel c): Evidence from the assessment of radiative forcing and climate sensitivity. The panel shows temperature changes from individual components of human influence, including emissions of greenhouse gases, aerosols and their precursors; land-use changes (land-use reflectance and irrigation); and aviation contrails. Whiskers show very likely ranges. Estimates account for both direct emissions into the atmosphere and their effect, if any, on other climate drivers. For aerosols, both direct (through radiation) and indirect (through interactions with clouds) effects are considered. {6.4.2, 7.3}

Due to the surge in CO2 levels, weather and climate patterns too have been impacted, and especially so due to human activity. “Climate change is already affecting every region on Earth, in multiple ways. The changes we experience will increase with additional warming,” said IPCC Working Group I Co-Chair Panmao Zhai.

Heatwaves have become more frequent and severe across most land masses since the 1950s, while the frequency and intensity of cold waves have reduced. Most land masses have also witnessed frequent and intense precipitation since the 1950s. Meanwhile, some regions experienced droughts due to increased land evapotranspiration.

Exhibit 3: Synthesis of assessed observed and attributable regional changes

Note: The IPCC AR6 WGI inhabited regions are displayed as hexagons with identical size in their approximate geographical location (see legend for regional acronyms). All assessments are made for each region as a whole and for the 1950s to the present. Assessments made on different time scales or more local spatial scales might differ from what is shown in the figure. The colours in each panel represent the four outcomes of the assessment on observed changes. White and light grey striped hexagons are used where there is low agreement in the type of change for the region as a whole, and grey hexagons are used when there is limited data and/or literature that prevents an assessment of the region as a whole. Other colours indicate at least medium confidence in the observed change. The confidence level for the human influence on these observed changes is based on assessing trend detection and attribution and event attribution literature, and it is indicated by the number of dots: three dots for high confidence, two dots for medium confidence and one dot for low confidence (filled: limited agreement; empty: limited evidence). Panel a) For hot extremes, the evidence is mostly drawn from changes in metrics based on daily maximum temperatures; regional studies using other indices (heatwave duration, frequency and intensity) are used in addition. Red hexagons indicate regions where there is at least medium confidence in an observed increase in hot extremes. Panel b) For heavy precipitation, the evidence is mostly drawn from changes in indices based on one-day or five-day precipitation amounts using global and regional studies. Green hexagons indicate regions where there is at least medium confidence in an observed increase in heavy precipitation. Panel c) Agricultural and ecological droughts are assessed based on observed and simulated changes in total column soil moisture, complemented by evidence on changes in surface soil moisture, water balance (precipitation minus evapotranspiration) and indices driven by precipitation and atmospheric evaporative demand. Yellow hexagons indicate regions where there is at least medium confidence in an observed increase in this type of drought and green hexagons indicate regions where there is at least medium confidence in an observed decrease in agricultural and ecological drought.

Temperatures will only rise further

“It has been clear for decades that the Earth’s climate is changing, and the role of human influence on the climate system is undisputed,” said Valérie Masson-Delmotte, IPCC Working Group I Co-Chair. Five emission scenarios have been used by the report to project possible future climate patterns. Across all listed scenarios, global surface temperatures will continue to rise until at least the mid-century. Global temperatures will exceed 2°C by end-21st century unless there are active reductions in CO2 and GHGs concentration levels.

Exhibit 4: Future anthropogenic emissions of key drivers of climate change and warming contributions by groups of drivers for the five illustrative scenarios

Note: The five scenarios are SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5. Panel a) Annual anthropogenic (human-caused) emissions over the 2015–2100 period. Shown are emissions trajectories for carbon dioxide (CO2) from all sectors (GtCO2/yr) (left graph) and for a subset of three key non-CO2 drivers considered in the scenarios: methane (CH4, MtCH4/yr, top-right graph), nitrous oxide (N2O, MtN2O/yr, middle-right graph) and sulfur dioxide (SO2, MtSO2/yr, bottom-right graph, contributing to anthropogenic aerosols in panel b). Panel b) Warming contributions by groups of anthropogenic drivers and by scenario are shown as change in global surface temperature (°C) in 2081–2100 relative to 1850–1900, with indication of the observed warming to date. Bars and whiskers represent median values and the very likely range, respectively. Within each scenario bar plot, the bars represent total global warming (°C; total bar) (see Table SPM.1) and warming contributions (°C) from changes in CO2 (CO2 bar), from non-CO2 greenhouse gases (non-CO2 GHGs bar; comprising well-mixed greenhouse gases and ozone) and net cooling from other anthropogenic drivers (aerosols and land-use bar; anthropogenic aerosols, changes in reflectance due to land-use and irrigation changes, and contrails from aviation; see Figure SPM.2, panel c, for the warming contributions to date for individual drivers). The best estimate for observed warming in 2010–2019 relative to 1850–1900 (see Figure SPM.2, panel a) is indicated in the darker column in the total bar. Warming contributions in panel b are calculated as explained in Table SPM.1 for the total bar. For the other bars the contribution by groups of drivers are calculated with a physical climate emulator of global surface temperature which relies on climate sensitivity and radiative forcing assessments.

Even considering a very low GHG emissions scenario, global surface temperatures will be higher by 1.0-1.8°C between 2081 and 2100 as compared with the 1850-1900 period. Meanwhile, the global warming level of 2°C will be exceeded within the 21st century under the high and very high GHG emissions scenario, when compared to the decades between 1850–1900.

Exhibit 5: Changes in global surface temperature

Note: Changes in global surface temperature, which are assessed based on multiple lines of evidence, for selected 20-year time periods and the five illustrative emissions scenarios considered. Temperature differences relative to the average global surface temperature of the period 1850–1900 are reported in °C. This includes the revised assessment of observed historical warming for the AR5 (UN IPCC’s Fifth Assessment Report) reference period 1986–2005, which in AR6 (UN IPCC’s Sixth Assessment Report) is higher by 0.08 [–0.01 to 0.12] °C than in the AR5. Changes relative to the recent reference period 1995–2014 may be calculated approximately by subtracting 0.85°C, the best estimate of the observed warming from 1850–1900 to 1995–2014.

Land surfaces will continue to become warmer by 1.4-1.7 times in comparison to ocean surfaces. The Arctic, meanwhile, will become two times warmer than the global surface temperature. With every additional 0.5°C of global warming, the frequency and intensity of heatwaves, precipitation, agricultural and ecological droughts will increase in certain regions such as the mid-latitude and semi-arid regions. These areas will register even warmer temperature – about 1.5 to 2 times the rate of global warming.

Exhibit 6: Projected changes in the intensity and frequency of hot temperature extremes over land, extreme precipitation over land, and agricultural and ecological droughts in drying regions

Note: Projected changes are shown at global warming levels of 1°C, 1.5°C, 2°C, and 4°C and are relative to 1850-1900 representing a climate without human influence. The figure depicts frequencies and increases in intensity of 10- or 50-year extreme events from the base period (1850-1900) under different global warming levels. Hot temperature extremes are defined as the daily maximum temperatures over land that were exceeded on average once in a decade (10-year event) or once in 50 years (50-year event) during the 1850–1900 reference period. Extreme precipitation events are defined as the daily precipitation amount over land that was exceeded on average once in a decade during the 1850–1900 reference period. Agricultural and ecological drought events are defined as the annual average of total column soil moisture below the 10th percentile of the 1850–1900 base period. These extremes are defined on model grid box scale. For hot temperature extremes and extreme precipitation, results are shown for the global land. For agricultural and ecological drought, results are shown for drying regions only, which correspond to the AR6 regions in which there is at least medium confidence in a projected increase in agricultural/ecological drought at the 2°C warming level compared to the 1850–1900 base period in CMIP6. These regions include W. North-America, C. North-America, N. Central-America, S. Central-America, Caribbean, N. South-America, N.E. South-America, South-American-Monsoon, S.W. South-America, S. South-America, West & Central-Europe, Mediterranean, W. Southern-Africa, E. Southern-Africa, Madagascar, E. Australia, S. Australia (Caribbean is not included in the calculation of the figure because of the too small number of full land grid cells). The non-drying regions do not show an overall increase or decrease in drought severity. Projections of changes in agricultural and ecological droughts in the CMIP5 multi-model ensemble differ from those in CMIP6 in some regions, including in part of Africa and Asia. Assessments on projected changes in meteorological and hydrological droughts are provided in Chapter 11. In the ‘frequency’ section, each year is represented by a dot. The dark dots indicate years in which the extreme threshold is exceeded, while light dots are years when the threshold is not exceeded. Values correspond to the medians (in bold) and their respective 5–95% range based on the multi-model ensemble from simulations of CMIP6 under different SSP scenarios. For consistency, the number of dark dots is based on the rounded-up median. In the ‘intensity’ section, medians and their 5–95% range, also based on the multi-model ensemble from simulations of CMIP6, are displayed as dark and light bars, respectively. Changes in the intensity of hot temperature extremes and extreme precipitations are expressed as degree Celsius and percentage. As for agricultural and ecological drought, intensity changes are expressed as fractions of standard deviation of annual soil moisture.

The global water cycle will continue to intensify with increases in global temperatures. Regions with warmer climate may face very wet and very dry weather depending on regional atmospheric changes, including monsoon and storm tracks. Countries in South and Southeast Asia, East Asia and West Africa are expected to receive increased monsoon precipitation in the mid- to long-term scenario.

Amid an increasing CO2 emissions scenario, the ocean and land carbon sinks will become less effective in slowing the accumulation of CO2 in the atmosphere. The rate at which land masses and oceans absorb CO2 emissions will decrease in the second half of the 21st century.

Exhibit 7: Cumulative anthropogenic CO2 emissions taken up by land and ocean sinks by 2100 under the five illustrative scenarios

Note: The cumulative anthropogenic (human-caused) carbon dioxide (CO2) emissions taken up by the land and ocean sinks under the five illustrative scenarios (SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5) are simulated from 1850 to 2100 by CMIP6 climate models in the concentration-driven simulations. Land and ocean carbon sinks respond to past, current and future emissions, therefore cumulative sinks from 1850 to 2100 are presented here. During the historical period (1850-2019) the observed land and ocean sink took up 1430 GtCO2 (59% of the emissions). The bar chart illustrates the projected amount of cumulative anthropogenic CO2 emissions (GtCO2) between 1850 and 2100 remaining in the atmosphere (grey part) and taken up by the land and ocean (coloured part) in the year 2100. The doughnut chart illustrates the proportion of the cumulative anthropogenic CO2 emissions taken up by the land and ocean sinks and remaining in the atmosphere in the year 2100. Values in % indicate the proportion of the cumulative anthropogenic CO2 emissions taken up by the combined land and ocean sinks in the year 2100. The overall anthropogenic carbon emissions are calculated by adding the net global land use emissions from CMIP6 scenario database to the other sectoral emissions calculated from climate model runs with prescribed CO2 concentrations33. Land and ocean CO2 uptake since 1850 is calculated from the net biome productivity on land, corrected for CO2 losses due to land-use change by adding the land-use change emissions, and net ocean CO2 flux.

Changes in the ocean, ice sheets and global sea levels, caused due to past and future GHG emissions, will remain irreversible for centuries to millennia. Mountain and polar glaciers will continue to melt. By 2100, the global mean sea level will have risen by 0.28 to 0.55 m in comparison to 1995-2014 levels.

Exhibit 8: Selected indicators of global climate change under the five illustrative scenarios

Note: The projections for each of the five scenarios are shown in colour. Shades represent uncertainty ranges – more detail is provided for each panel below. The black curves represent the historical simulations (panels a, b, c) or the observations (panel d). Historical values are included in all graphs to provide context for the projected future changes. Panel a) Global surface temperature changes in °C relative to 1850–1900. These changes were obtained by combining CMIP6 model simulations with observational constraints based on past simulated warming, as well as an updated assessment of equilibrium climate sensitivity (see Box SPM.1). Changes relative to 1850–1900 based on 20-year averaging periods are calculated by adding 0.85°C (the observed global surface temperature increase from 1850–1900 to 1995–2014) to simulated changes relative to 1995–2014. Very likely ranges are shown for SSP1-2.6 and SSP3-7.0. Panel b) September Arctic Sea ice area in 106 km2 based on CMIP6 model simulations. Very likely ranges are shown for SSP1-2.6 and SSP3-7.0. The Arctic is projected to be practically ice-free near mid-century under mid and high GHG emissions scenarios. Panel c) Global ocean surface pH (a measure of acidity) based on CMIP6 model simulations. Very likely ranges are shown for SSP1-2.6 and SSP3-7.0. Panel d) Global mean sea level change in meters relative to 1900. The historical changes are observed (from tide gauges before 1992 and altimeters afterwards), and the future changes are assessed consistently with observational constraints based on emulation of CMIP, ice sheet, and glacier models. Likely ranges are shown for SSP1-2.6 and SSP3-7.0. Only likely ranges are assessed for sea level changes due to difficulties in estimating the distribution of deeply uncertain processes. The dashed curve indicates the potential impact of these deeply uncertain processes. It shows the 83rd percentile of SSP5-8.5 projections that include low-likelihood, high-impact ice sheet processes that cannot be ruled out; because of low confidence in projections of these processes, this curve does not constitute part of a likely range. Changes relative to 1900 are calculated by adding 0.158 m (observed global mean sea level rise from 1900 to 1995–2014) to simulated and observed changes relative to 1995–2014. Panel e): Global mean sea level change at 2300 in meters relative to 1900. Only SSP1-2.6 and SSP5-8.5 are projected at 2300, as simulations that extend beyond 2100 for the other scenarios are too few for robust results. The 17th–83rd percentile ranges are shaded. The dashed arrow illustrates the 83rd percentile of SSP5-8.5 projections that include low-likelihood, high-impact ice sheet processes that cannot be ruled out. Panels b) and c) are based on single simulations from each model, and so include a component of internal variability. Panels a), d) and e) are based on long-term averages, and hence the contributions from internal variability are small.

Limit the climate crisis

Limiting cumulative CO2 emissions is one possible way of containing human influenced global warming. But this will require global CO2 emissions to be reduced to net zero, including strong reductions in other GHG emissions. In addition, stemming the use of aerosols will arrest aerosol emissions, leading to better air quality and reduced warming effects.

There is a clear link between CO2 emissions and global warming. Each 1,000 GtCO2 of cumulative CO2 emissions is likely to cause an increase of 0.27-0.63°C in global surface temperatures.

Exhibit 9: Near-linear relationship between cumulative CO2 emissions and the increase in global surface temperature

Note: Top panel: Historical data (thin black line) shows observed global surface temperature increase in °C since 1850–1900 as a function of historical cumulative carbon dioxide (CO2) emissions in GtCO2 from 1850 to 2019. The grey range with its central line shows a corresponding estimate of the historical human-caused surface warming (see Figure SPM.2). Coloured areas show the assessed very likely range of global surface temperature projections, and thick coloured central lines show the median estimate as a function of cumulative CO2 emissions from 2020 until year 2050 for the set of illustrative scenarios (SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5, see Figure SPM.4). Projections use the cumulative CO2 emissions of each respective scenario, and the projected global warming includes the contribution from all anthropogenic forcers. The relationship is illustrated over the domain of cumulative CO2 emissions for which there is high confidence that the transient climate response to cumulative CO2 emissions (TCRE) remains constant, and for the time period from 1850 to 2050 over which global CO2 emissions remain net positive under all illustrative scenarios as there is limited evidence supporting the quantitative application of TCRE to estimate temperature evolution under net negative CO2 emissions. Bottom panel: Historical and projected cumulative CO2 emissions in GtCO2 for the respective scenarios.

Lowering global CO2 emissions to net zero is critical towards stabilising CO2-induced global surface temperature increases. Anthropogenic CO2 removal (CDR) is effective in removing CO2 from the atmosphere, which is then stored in reservoirs. CDR removal is critical in achieving global net zero emissions, resulting in lower atmospheric CO2 concentration and reversed ocean surface acidification. If CDR is achieved and sustained, CO2-induced surface temperature increases can be gradually reversed.

Mr Zhai reiterated that, “Stabilising the climate will require strong, rapid and sustained reductions in greenhouse gas emissions, and reaching net zero CO2 emissions.” A failure to heed the climate change clarion call can lead to catastrophic consequences.

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