climate change

john

Climate change and climate variability

• CLIMATE- The statistics of weather prevailing in a location

• CLIMATE VARIABILITY- Shorter term departures from average climate

• CLIMATE CHANGE- Long-term changes to these statistics

ENSO- IMPACTS

West Pacific:

• Droughts (China 1977-778)

• Wildfires (Australia, SE Asia 1997-98- 5 million ha of forest lost)

East Pacific:

• Floods in Peru (1997-98)

• 500,000 homeless

• Utility damage: $2.6 billion

• Collapse Fishing industry

Natural climate variability- MITIGATION

• Predictions significantly improved

• Early warning and action

• Peru 2015: declared 60-day state of emergency and spent $20 million on flood and drought prevention

Natural climate variability- CHALLENGES

• Need improved understanding of ENSO dynamics and likelihood

• Better understanding of ENSO signatures and how they unfold into socio-economic impacts

• Uncertainty over how ENSO may be affected in the future (“Super El Nino”, increased frequency)

Thermohaline Circulation- YOUNG DRYAS

12,900- 11,700 years BP

Cooling in NA following post ice-age warming
Glaciers in Scotland and Wales

Thermohaline Circulation- FUTURE IMPLICATIONS

Hansen et al. (2016)

• Ice sheet models forecast less than 1m sea level rise by 2100 but most lack processes that result in exponential growth of ice loss

• Increases in Antarctic and Greenland ice loss mean exponential increases in freshwater input to the ocean surfaces

• Ocean becomes more stratified with cold fresh water (light) at the surface and warmer salty (heavy) water a the bottom

• Positive feedback- Antarctic ice shelves are in contact with deep (warmer) water= surface air temp drops

Anthropogenic Climate Change- CAUSES

El Niño Southern Oscillation

EL NINO:

• Ocean

• Warm surface waters off the coast of Peru lead to reduced fish harvests in some years

• Natural climate variability

• Recurring pattern- 2-7 years

SOUTHERN OSCILLATION:

• Atmosphere

• Normal years: high pressure in the central pacific, low pressure to the West (Australia)

• Opposite in some years

Trade winds collapse- cold upwelling at equator weakens- similar temperature on the east and west edges of the pacific

ENSO facts

• linked to droughts, floods, landslides, storms, wildfires

• hottest years on record

• floods in southern us

• atlantic hurricane activity

• disease outbreaks (mosquito viral diseases in Australia)

• Dry conditions in the Sahel

2023/24 El Nino

• transition from el nino to enso neutral is likely by april-june 2024 (79%)

• increasing odds of La Nina developing in June-August 2024 (55%)

North Atlantic Oscillation (NAO)

• index based on the surface sea-level pressure difference between the Subtropical High (Azores) and Subpolar Low (Iceland)

• Both phases are associated with the basin-wide changes in intensity and location of NA jet stream and storm track

• Considerable inter-seasonal and inter-annual variability

Nine Principal Climate Oscillations

1. El Nino Southern Oscillation

2. Pacific Decadal Oscillation

3. North Pacific Oscillation

4. North Pacific Gyre Oscillation

5. Atlantic Multidecadal Oscillation

6. North Atlantic Oscillation

7. Arctic Oscillation

8. Antarctic Oscillation

9. Indian Ocean Oscillation

Thermohaline Circulation

Freezing of surface ocean water leaving denser salty water which sinks to form deep water

This + winds= Atlantic Meridional Overturning Circulation (AMOC)

Supplies 1/3 of Europe’s heat energy

Anthropogenic climate change

2024- warmest year on record (+1.55 degrees)

Several of the past 2 decades are in top 10

likely to reach 1.5 degrees between 2030 and 2052

Greenhouse effect

Impacts on Natural Systems

• Northern hemisphere spring snow cover- decrease

• Arctic summer sea ice extent- significant decrease

• Change in global average upper ocean heat constant- increase

• Global average sea level change- significant increase

Impacts on society

Abrupt events-

• extreme weather events

• flooding

• wildfires

• disease

Prolonged hazards-

• food security

• water resources

• biodiversity

• conflict

• migration

future

• models are used to predict impacts, but the outcomes depend on emission scenarios

• extreme events may trigger but do not create disasters