Climate change

Climate change: A global crisis demanding urgent attention

Imagine a world where the very air we breathe and the water we drink are under threat, all because of human activities that have been going on for centuries. That’s the reality we face today as climate change continues to reshape our planet in ways both subtle and catastrophic. The rise in global temperatures, driven by a 50% increase in carbon dioxide levels since the Industrial Revolution, is not just a scientific fact—it’s a stark warning sign that demands immediate action.

Climate change impacts are far-reaching and devastating. From expanding deserts to heat waves, wildfires, and rising sea levels, these effects are already being felt around the globe. The World Health Organization considers climate change a major threat to global health in the 21st century, with increased flooding, extreme heat, food and water scarcity, disease, and economic loss as some of its most pressing consequences.

But it’s not just about the future; the present is already dire. Since the start of the 21st century, we’ve seen unprecedented warming trends, with 2023 being the warmest year on record. Limiting global warming to 1.5°C would require halving emissions by 2030 and achieving net-zero emissions by 2050. Phasing out fossil fuel use can be achieved through conserving energy and switching to carbon-free energy sources like wind, solar, hydro, and nuclear power.

These clean energy solutions are not only crucial for reducing greenhouse gas emissions but also offer a path towards sustainable development. Cleanly generated electricity can replace fossil fuels for powering transportation, heating buildings, and running industrial processes. Carbon can also be removed from the atmosphere by increasing forest cover and farming with methods that capture carbon in soil.

Before the 1980s, it was unclear whether the warming effect of increased greenhouse gases was stronger than the cooling effect of airborne particulates in air pollution. However, since then, terms like ‘global warming’ and ‘climate change’ have become more common, reflecting a growing understanding of the issue.

Over the last few million years, the climate cycled through ice ages. One of the hotter periods was the Last Interglacial, around 125,000 years ago. Since the Industrial Revolution, there has been a marked increase in temperature due to the accumulation of greenhouse gases and controls on sulfur pollution. Multiple independent datasets show a worldwide increase in surface temperature, with the 2014–2023 decade averaging 1.19°C above the pre-industrial baseline.

Regional differences in warming rates exist due to regional characteristics and greenhouse gas distribution. The Northern Hemisphere has warmed faster than other regions, particularly the Arctic, which has increased at three to four times the global rate. Future temperature projections indicate an 80% chance that global temperatures will exceed 1.5°C between 2024 and 2028.

The IPCC expects the 20-year average global temperature to exceed +1.5 °C in the early 2030s. Global warming projections include a range of outcomes depending on emissions scenarios: 1.0–1.8 °C by 2100 under low emissions, 2.1–3.5 °C by 2100 under intermediate emissions, and 3.3–5.7 °C by 2100 under high emissions.

Warming will continue past 2100 in the intermediate and high emission scenarios. A global surface temperature increase of similar magnitude to millions of years ago is expected by year 2300. Global warming can be kept below 1.5 °C with a 50% chance if emissions after 2023 do not exceed 200 gigatonnes of CO2, corresponding to around 4 years of current emissions.

To stay under 2.0 °C, the carbon budget is 900 gigatonnes of CO2, or 16 years of current emissions. The climate system experiences various natural cycles and external forcings that contribute to global temperature rise, such as changes in greenhouse gas concentrations, solar luminosity, volcanic eruptions, and variations in the Earth’s orbit around the Sun.

Greenhouse gases are transparent to sunlight but absorb a portion of it, trapping heat near the Earth’s surface and warming it over time. While water vapour (≈50%) and clouds (≈25%) contribute significantly to the greenhouse effect, they are mostly considered feedbacks due to their temperature-dependent changes in concentration.

Human activity since the Industrial Revolution has increased greenhouse gas concentrations, particularly CO2 and methane, with levels 50% higher than 1750. Global human-caused emissions in 2019 were equivalent to 59 billion tonnes of CO2, with emissions primarily from fossil fuel burning, deforestation, and industrial processes.

CO2 concentrations have increased to levels not seen in 14 million years due to human activity. Methane emissions come from livestock, manure, rice cultivation, landfills, wastewater, and coal mining, with methane lasting only 12 years in the atmosphere. CO2 lasts much longer, with some estimates suggesting it can take millions of years for CO2 to be stored in the Earth’s crust.

Land area unusable for humans accounts for 30% of the globe, with forests making up 26%, agricultural land 34%, and shrubland 10%. Deforestation has led to 27% of global warming due to permanent clearing, while temporary clearing accounts for 24%. Logging and wildfires account for the remaining percentage. Restoring degraded forests can recover their potential as carbon sinks.

Local vegetation cover impacts sunlight reflection and heat loss through evaporation. Deforestation modifies chemical compound release and wind patterns, influencing clouds and climate patterns. In tropic and temperate areas, forest restoration can make local temperatures cooler due to increased surface albedo. Globally, land use change has a slight cooling effect, primarily due to increases in surface albedo.

Around half of human-caused CO2 emissions have been absorbed by land plants and by the oceans. This fraction is not static, and if future CO2 emissions decrease, the Earth will be able to absorb up to around 70%. If they increase substantially, it’ll still absorb more carbon than now, but the overall fraction will decrease to below 40%.

A climate model is a representation of the physical, chemical, and biological processes that affect the climate system. Models include natural processes like changes in the Earth’s orbit, historical changes in the Sun’s activity, and volcanic forcing. Models are used to estimate the degree of warming future emissions will cause when accounting for the strength of climate feedbacks.

The environmental effects of climate change include gradual or rapid changes affecting oceans, ice, and weather. Droughts and heat waves increase in frequency since the 1950s, monsoonal precipitation increases in the Northern Hemisphere, and rainfall rate and intensity of hurricanes and typhoons increase.

Global sea level rise is occurring due to thermal expansion and melting glaciers. Sea level rose 4.8 cm per decade between 2014 and 2023. Projected sea level rise: 32–62 cm under low emission scenario, 44–76 cm under intermediate scenario, 65–101 cm under high emission scenario.

Climate change causes shrinking and thinning of Arctic sea ice, with ice-free summers expected at 1.5 °C warming. Oceans become more acidic and oxygen levels decrease, leading to the expansion of dead zones. Tipping points and long-term impacts include the risk of passing ‘tipping points’ increasing with global warming.

Greenland ice sheet melting accelerates above certain temperature thresholds, and collapse of major ocean currents and ecosystems can occur in decades. The result is an estimated total sea level rise of 2.3 meters per degree Celsius after 2000 years. Oceanic CO2 uptake is slow, leading to continued ocean acidification for hundreds to thousands of years.

The West Antarctic ice sheet appears committed to practically irreversible melting, increasing sea levels by at least 3.3 m over approximately 2000 years. Recent warming has driven many species poleward and towards higher altitudes. Global greening due to higher atmospheric CO2 levels is offset by heatwaves and droughts reducing ecosystem productivity.

Woody plant encroachment affects up to 500 million hectares globally, contributing to the expansion of drier climate zones. Climate change will likely result in extinction of many species. Heatwaves in oceans harm organisms such as corals, kelp, and seabirds. Ocean acidification makes it harder for marine calcifying organisms to produce shells and skeletons.

Coastal ecosystems are under stress, with almost half of global wetlands disappearing due to climate change and other human impacts. Plants face increased stress from damage by insects. The effects of climate change impact humans everywhere, with low-latitude, less developed areas facing the greatest risk.

The risks are unevenly distributed but generally greater for disadvantaged people in developing and developed countries. Extreme weather events affect public health and food security due to increased illness and death from temperature extremes. Climate change intensifies and frequency of extreme weather events, affecting transmission of infectious diseases like dengue fever and malaria.

By 2050, 14.5 million deaths are expected due to climate change, with 30% of the global population already living in areas where extreme heat and humidity lead to excess deaths. By 2100, up to 75% of the global population may live in such areas.

Climate change affects agricultural productivity, fisheries, and livestock headcounts, leading to decreased crop yields, negative impacts on fisheries, and potential declines in livestock populations by 7-10%. Annual climate-related deaths could reach over 9 million if emissions continue to increase.

Economic damages from climate change are severe, with the World Bank estimating that up to 120 million people could be driven into extreme poverty without adaptation. Marginalized people face worsened inequalities due to climate change, and indigenous communities are endangered by their land and ecosystems.

Women’s adaptive capacity is constrained by discriminatory norms and limited resources. Low-lying islands and coastal communities face statelessness and urban flooding due to sea level rise, which may become too severe for humans to adapt to in some regions.

With worst-case climate change, almost one-third of humanity may live in uninhabitable climates. Climate or environmental migration is expected due to sea level rise, extreme weather, and conflict over resources. Reducing greenhouse gas emissions can mitigate climate change by tripling pledges under the Paris Agreement within a decade to limit global warming to 2°C.

Limiting warming to 1.5°C requires far-reaching changes in energy, land, cities, transport, buildings, and industry. Renewable energy is key to mitigating climate change, with solar radiation modification being a possible supplement to deep reductions in emissions. Fossil fuel use is expected to peak before 2030, with coal use declining sharply.

Renewables generated 86% of new electricity in 2023, but their future growth forecasts are limited compared to nuclear and hydropower. To achieve carbon neutrality by 2050, renewable energy would dominate electricity generation, rising to 85% or more. Investment in coal would be eliminated and coal use nearly phased out by 2050.

Energy sources for heating and transport need to switch to low-carbon alternatives, including electric vehicles, public transit, and heat pumps. There are obstacles to the growth of clean energy, such as intermittent renewable production and social concerns surrounding hydropower. Low-carbon energy improves human health and can save millions of lives per year if climate goals are met.

Reducing energy demand through efficiency measures is crucial for achieving climate goals, requiring significant investment in energy efficiency. In the building sector, focus is on better design and higher energy efficiency through technologies like heat pumps.

Agriculture and industry face a triple challenge of limiting emissions while meeting food demand; actions include reducing demand for food, increasing land productivity, protecting forests, and reducing agricultural production emissions. Livestock are responsible for 3/4ths of agriculture emissions; steel and cement production drive about 13% of industrial CO2 emissions.

Carbon capture and storage (CCS) has a limited role in reducing emissions due to high costs and deployment limits. Natural carbon sinks can be enhanced through practices like reforestation, afforestation, soil conservation, and forest restoration. Bioenergy with carbon capture and storage (BECCS) offers potential for net negative emissions, but its effectiveness is uncertain.

Adaptation is key to adjusting to climate change, but transformative adaptation requires significant investment; capacity and potential vary across regions and populations. There is a significant gap between necessary and available finance for climate change adaptation. Adaptation strategies include avoiding at-risk areas, learning to live with increased flooding, building flood controls, and managed retreat.

Economic barriers prevent some from tackling heat impacts, while agriculture can adapt through sustainable diets, diversification, erosion control, and genetic improvements. Insurance, education, migration, early warning systems, and restoring natural ecosystems can reduce climate vulnerability. However, there are synergies between adaptation and mitigation, but also trade-offs, such as increased energy demand with air conditioning use.

Climate change disproportionately affects vulnerable countries that have contributed minimally to global emissions, raising questions about justice and fairness. Limiting global warming is linked to achieving Sustainable Development Goals, including eradicating poverty and reducing inequalities.

Climate change geopolitics is complex, framed often as a free-rider problem, but with localized benefits from mitigation efforts. Ecosystems adapt to climate change through human intervention, such as increasing connectivity between ecosystems, introducing species to favorable climates, and protecting and restoring natural areas.

These actions also support human adaptation via ecosystem-based adaptation, such as restored fire regimes reducing catastrophic fires and providing carbon sinks. Fossil fuel net importers win economically from switching to clean energy, causing stranded assets for net exporters.

A range of policies are being used to reduce emissions, including carbon pricing, direct global fossil fuel subsidies, and regulations on vehicles and heavy industry. Ending these subsidies could save $5.2 trillion and lead to a 28% reduction in carbon emissions and a 46% reduction in air pollution deaths.

Climate justice policy aims to address human rights issues and social inequality, with wealthy nations paying for climate adaptation costs and benefiting poorer countries. The top 10% of people are responsible for 50% of global emissions, while the bottom 50% are responsible for just 8%.

Nearly all countries are parties to the 1994 UN Framework Convention on Climate Change (UNFCCC), which aims to prevent dangerous human interference with the climate system and provide a framework for protocols that restrict emissions. The Kyoto Protocol and Copenhagen Accord have been used to negotiate global agreements, but their goals have been criticized as too low.

Carbon can be priced in various ways including carbon taxes and emissions trading systems with some countries requiring utilities to increase the share of renewables in power production. Ending direct global fossil fuel subsidies could save money that could be used to support clean energy. 3 billion were delivered. Only in 2023 the target is expected to be achieved.

In 2015 all UN countries negotiated the Paris Agreement, which aims to keep global warming well below 2.0 °C and contains an aspirational goal of keeping warming under 1.5 °C. The agreement replaced the Kyoto Protocol. Countries have to regularly set ever more ambitious goals and reevaluate these goals every five years.

The 1987 Montreal Protocol, an international agreement to phase out production of ozone-depleting gases, has had benefits for climate change mitigation. Several ozone-depleting gases like chlorofluorocarbons are powerful greenhouse gases, so banning their production and usage may have avoided a temperature rise of 0.5 °C–1.0 °C.

In the early 20th century, scientists such as Gilbert Plass, Hans Suess, Roger Revelle, and Charles Keeling contributed to the development of climate models and evidence that CO2 levels were rising. The 1988 IPCC report marked a turning point in the scientific consensus on human-caused climate change, with agreement reaching over 99% by 2019.

National science academies have called for action to protect people against climate change impacts, and the 2021 IPCC Assessment Report stated that it is ‘unequivocal’ that climate change is caused by humans. The fight against climate change requires a collective effort from every individual, community, and nation. We must act now to ensure a sustainable future for generations to come.