Ecocide (the killing of ecologies by humans) results at least in widespread, irreversible biodiversity loss (species loss) and the climate crisis (the emergency of climate change). This article focuses on the climate crisis.

What Is the Climate Crisis (Climate Change)?

What is the climate crisis, i.e., the emergency of climate change? Before we can understand the crisis, we need to define some important concepts, notably: climate and climate system.

Climate

Climate can be defined as the average state of the atmosphere for a given time period (e.g.¸ hour, day, month, season, year, decade) for a specified geographical region. Climate descriptors include atmospheric temperature, humidity, precipitation, and conditions at the Earth’s surface, such as ocean temperatures and snow cover. It should be noted that weather is not the same as climate: weather involves the description of the atmospheric condition at a single point in time, while climate can be thought of as an average of weather conditions over a period of time, including the probability for distributions around this average.^[1]

Climate System

The climate system consists of five components: atmosphere, ocean, land surface, ice and snow surfaces (both land and ocean areas), and biosphere (both terrestrial and marine). The components interact with each other. There are also other factors that contribute to determining climate, considered ‘external’ factors, including the sun (including electromagnetic radiation from the sun (sunlight) and activities within or involving the sun), land-ocean distribution, land and ocean topography, and the basic composition of the atmosphere and ocean.^[1]

Climate Change

Climate change is generally defined as the change in climate attributed directly or indirectly to human activity, which, in addition to natural climate variability, is observed over comparable time periods. One of the main indicators of climate change is global warming; the Earth’s average surface air temperature has increased by about 1°C since 1900, with over half of the increase occurring since the mid-1970s.^[2]

What Contributes to Global Warming?^[2]

The sun serves as the primary energy source for all life and the Earth’s climate. Part of the incoming sunlight is reflected directly back into space, especially by ice and clouds, and the rest is absorbed by the surface and the atmosphere. Much of this absorbed solar energy is re-emitted as heat (infrared radiation); the atmosphere in turn absorbs and re-radiates heat, some of which escapes to space. Any disturbance to this balance of incoming and outgoing energy affects the climate.

If all heat energy emitted from the surface passed through the atmosphere directly into space, Earth’s average surface temperature would be tens of degrees colder than today. Greenhouse gases in the atmosphere, such as carbon dioxide (CO₂), water vapor, methane (CH₄), and nitrous oxide (N₂O), act to make the Earth’s surface much warmer than this because they absorb and emit heat energy in all directions (including downwards), keeping Earth’s surface and lower atmosphere warm.

Greenhouse gases emitted by human activities alter Earth’s energy balance and thus its climate. The biggest contributor to the planet’s warming has been determined to be increases in CO₂. Direct measurements of CO₂ in the atmosphere and in air trapped in ice show that atmospheric CO₂ increased by more than 40% from 1800 (the onset of the industrial revolution) to 2019. Measurements of different forms of carbon (isotopes) reveal that this increase is due to human activities. Other greenhouse gases (mostly, methane and nitrous oxide) are also increasing due to human activity.

Sources of some human-emitted greenhouse gases:

• Carbon dioxide (CO₂). Combustion of fossil fuels, cement production, deforestation (reduces CO₂ uptake by trees), and other land use changes.
• Methane (CH₄). Raising livestock, growing paddy rice, filling landfills, using natural gas.
• Nitrous oxide (N₂O). Industrial agriculture using synthetic nitrogen-based fertilizers, land use changes.
• Halocarbons (including chlorofluorocarbons (CFCs)) and some replacements. They damage the ozone layer (a layer in the Earth’s stratosphere that absorbs most of the ultraviolet radiation reaching the earth from the sun)

Why Is Climate Change of Concern?

All major climate changes, whether natural or man-made, are disruptive. Past climate changes led to the extinction of many species, migrations, and significant alterations in the land surface and ocean circulation. However, the speed at which the climate is changing currently is faster than most past events, making it increasingly difficult for human peoples and ecologies to adapt. Warming temperatures due to carbon pollution (rising CO₂ levels) have several deleterious effects, including: widespread melting of snow and ice (glaciers) and rising global sea levels, increasing average air and ocean temperatures, ocean acidification (affecting marine organisms), changing atmospheric and ocean circulation (influencing rainfall and wind patterns), extreme weather events (e.g., floods, forest fires, droughts, cyclones, hurricanes), plant/tree death, and changes in organismal behavioral pattens, like bird migration.^[3]

The average temperature  over the past 30 years has been rising by 0.2°C per decade. The frequency and intensity of extreme weather events, and accompanying fires, floods, and droughts have increased in the past 50 years, while the global average sea level has risen by 16-21 cm since 1900 (and at a rate of >3 mm per year over the past two decades).

These changes have contributed to widespread impacts in many aspects of biodiversity, including population dynamics, community structure, species distribution, phenology, and ecosystem function. Observational evidence indicates that the effects are accelerating in marine, terrestrial and freshwater ecosystems and are already impacting agriculture, aquaculture, fisheries, and nature’s contributions to people (ecosystem services)^[4].

The compounding effects of drivers such as overexploitation of resources, pollution, climate change, land-/sea-use change, and invasive alien species are likely to exacerbate the negative impacts on nature. These can be seen in different ecosystems, including coral reefs, the Arctic systems, and savannas. In particular, marine plastic pollution, has increased tenfold since 1980 (negatively impacting biodiversity and humans through food chains). Untreated urban and rural waste, pollutants from industrial, mining and agricultural activities, greenhouse gas emissions, toxic dumping, and oil spills have had strong negative effects on soil, freshwater and marine water quality, and on the global atmosphere. Cumulative records of alien species have increased by 40% since 1980, associated with trends of increased trade and human population growth. Nearly 20% of the Earth’s surface is at risk of plant and animal invasions, impacting native species, ecosystem functions, and ecosystem services, as well as economies and human health. Furthermore, the rate of introduction of new invasive alien species seems higher than ever before and shows no signs of slowing.^[2]

[1] D.D. Houghton, Introduction to Climate Change: Lecture Notes for Meteorologists, Secretariat of the World Metereological Organization, Geneva, Switzerland: WMO-No. 926 (2002).
 

[2] Climate Change Evidence & Causes: Update 2020, Royal Society and the US National Academy of Sciences (2020).

[3] Climate Change, National Environment Commission, Royal Government of Bhutan (2011).
 

[4] S. Mukherjee & K. Mitra, FiveBecomings: Understanding Project Impact Through the Ecosystem Services Lens, Ecosymbionts all Regenerate Together (EaRTh): DOI-EaRTh082025-005 (28 Aug., 2025).