Climate change is reshaping our world. Global temperatures have risen, sea levels are creeping up, and extreme weather events are becoming more frequent. These changes are linked to human activities, particularly the burning of fossil fuels and deforestation.

Looking ahead, climate projections paint a concerning picture. Temperatures are expected to rise further, precipitation patterns will shift, and sea levels will continue to climb. These changes will impact ecosystems, agriculture, and human health in profound ways.

Observed Climate Changes

Changes in global climate indicators

• Global temperature
  • Average global surface temperature increased by ~1.1°C since pre-industrial times (late 19th century)
  • Warming accelerated in recent decades with warmest years on record in 21st century (2016, 2020)
• Sea level
  • Global mean sea level risen by ~21-24 cm since 1880 due to thermal expansion of oceans and melting of land-based ice (glaciers, ice sheets)
  • Rate of sea level rise increased in recent decades currently at ~3.4 mm per year (satellite data)
• Extreme weather events
  • Increased frequency and intensity of heatwaves and heavy precipitation events (floods, landslides)
  • More frequent and severe droughts in some regions (East Africa, Australia)
  • Intensification of tropical cyclones with higher maximum wind speeds and heavier rainfall (Hurricane Harvey, Typhoon Haiyan)

Evidence for human-caused climate change

• Temperature records
  • Instrumental temperature records show clear warming trend since late 19th century
  • Warming pattern consistent with expected response to increased greenhouse gas concentrations (CO2, methane)
• Ice core data
  • Ice cores provide record of past atmospheric composition and temperature (Antarctic, Greenland)
  • Data shows strong correlation between atmospheric CO2 concentrations and global temperature over past 800,000 years
  • Current CO2 levels unprecedented in ice core record indicating human influence (fossil fuel emissions, deforestation)
• Other evidence
  • Retreat of glaciers and ice sheets (Himalayas, Antarctica)
  • Shifts in species distributions and phenology (earlier spring events, poleward migration)
  • Changes in ocean temperature and acidity (warming, ocean acidification)

Projected Climate Changes

Climate projections under emission scenarios

• Temperature
  • Global average surface temperature projected to increase by 1.5-4.0°C by 2100 depending on emission scenario (RCP2.6 to RCP8.5)
  • Warming will be greater over land and at higher latitudes (Arctic amplification)
• Precipitation patterns
  • Changes in precipitation will vary regionally
  • Many dry regions expected to become drier while wet regions become wetter (Mediterranean, Amazon)
  • Increased likelihood of intense precipitation events (flash floods, landslides)
• Sea level
  • Global mean sea level projected to rise by 0.26-0.82 m by 2100 depending on emission scenario
  • Thermal expansion of oceans and melting of land-based ice contribute to sea level rise
  • Regional variations in sea level rise due to factors such as ocean circulation and land subsidence (Gulf Coast, Mekong Delta)

Impacts of climate change

• Ecosystems
  • Shifts in species distributions and altered timing of biological events (bird migration, insect emergence)
  • Increased risk of extinction for many species particularly those with limited ability to adapt or migrate (coral reefs, polar bears)
  • Changes in ecosystem structure and function such as altered food webs and nutrient cycling (permafrost thaw, ocean deoxygenation)
• Agriculture
  • Shifts in crop growing seasons and regions (longer growing seasons in high latitudes, reduced suitability in tropics)
  • Reduced yields in some areas due to increased heat stress, drought, and extreme weather events (maize, wheat)
  • Increased pest and disease pressure (locusts, coffee rust)
  • Positive effects in some high-latitude regions due to longer growing seasons (Canada, Russia)
• Human health
  • Increased heat-related illnesses and deaths (heatstroke, cardiovascular disease)
  • Spread of vector-borne diseases to new areas (malaria, dengue fever)
  • Reduced air quality and increased respiratory issues (ozone, particulate matter)
  • Food and water insecurity in some regions (Sub-Saharan Africa, South Asia)
  • Mental health impacts from displacement and loss of livelihoods (climate refugees, farmers)