Projecting Future Climate Change Flashcards
Fast Feedbacks
- immediate to 10’s of years response e.g water vapour
Slow feed backs
1,000’s to 10,000’s of years response
Orbital forcing
0.25W/m^2
This is not enough energy to raise global temperature by 5 degrees Celsius. This indicates there are fast and strong Feedbacks amplifying the small forcing
Carbon cycle
Positive and negative feedback
Acts as a fertiliser for vegetation
30% of the CO2 from humans have been taken up by the ocean and vegetation. It is also amplifying the global temperature increase
Target CO2 emissions
2 degrees Celsius is too high based on most recent research. There USA strong likelihood that the sea level response will be exponential and 29cm is not realistic
Models used to predict the 2 degree Celsius did not consider ice sheet decay = linear trajectory - exponential increase
Dust group
Absorbs and scatters incoming shortwave radiation. Fertilises the oceans. Glacial periods contain higher dust content. Derived from South America exposed continental shelves and due to increased aridity. Most of the dust reaching Antarctica is from South America
Temperature group
Hydrogen stable isotopes record temperature. Comparison from benthic O^18 from forums. Confirms temperature signal after 800Kyr
CO2 group
Glacials= oceans are colder holding more CO2. Less upwelling due to increased sea ice and dust fertilisation causes increase phytoplankton and CO2 drawdown
Pulling records together
Temperature and CO2 is the same
Dust leads up to 5,000 years in all of the records. Decrease I. Dust = change in winds or increase in sea level to reduce arid conditions.
One hypothesis for the rise in CO2 at the end of the last glacial maximum (termination) is that reduced iron (dust) supply to the southern ocean caused by the increase of 80-100ppm CO2
Qua ternary Glacial - interglacial cycles
The last 2.7Ma characterised by glacial - interglacial cycle
The period contains the highest variability throughout the cenozoic force by the milankovitch cycles
Glacial periods characteristics
- ice ages paced by changes in the earths orbit
- large parts of Eurasia and North America ice covered
- sea level = 130m lower
- global temperature ~6 degrees lower. They were cooler because greater ice albedo and greater land albedo (less vegetation)
- lower atmospheric GHGs
Conditions favourable for ice sheets
- accumulation rates exceed ablation
- temperature
Temperature and ice mass balance
Limited by cold air not being able to hold water. High latitudes = winter temperatures always cold.
Winter is NOT the critical season. It’s summer melting which controls ice sheet growth. No matter how much snow falls during winter, it can easily melt if the following summer is warm and ablation is rapid
Terminating ice ages
Ice sheets melt when summer Insolation is high =’axial tilt is high
The change in solar radiation due to milankovitch forcing is
One possibility is gas trapping in the ice
Gases trapped during ice sintering (sealing). Gases younger than host ice due to air diffusion up to 50m.
Accumulation rate determines the gas age. Range from 100 - 2,000 years
Future global and regional climate change
Climate projects are made using climate models with various ranges of sophistication. All climate models look at earth system changes for the year 2100 AD, include higher than current atmospheric CO2.
All models project similar changes over the next few decades, the magnitude of change for the mid 21st century depends on the emissions scenario trying to project until the end of the century with all showing increase in CO2
RCP2.6 CO2 emissions scenario
Mitigation scenario for energy and industry related CO2 emissions. Requires a 70% reduction in emissions. Without mitigation scenarios result in 2.6W:m^2 forcing
Global average surface temperature
Surface warming likely to exceed 2 degrees and warning will continue to increase after 2100 for all scenarios except RCP2.6. RCP2.8 = over 11 degrees if not action is taken. Warming will not be regionally uniform.
How do climate models work
A climate model is a mathematical representation of how ocean, land and atmosphere interact. The Earth’s component are divided into a set of boxes then layers. Most recent models include hydrological and carbon cycle.
Super computers sun models that incorporate many factors and great spatial detail. Evolution enabled by an increase in computational capacity. Super computer speeds have increased by a factor of a. Ill on since 1970s
Super computer mid 1980s
- low resolution
- prescribed ice
Super computer early 1990s
- first assessment report of the IPCC
- atmospheric models were coupled to a “swap” or “slab” ocean
Super computer 1996
- 2nd assessment of the IPCC
- additional aerosols = sulphate, volcanic activity
Super computer 2001
- 3rd assessment report of the IPCC
- Rivers, carbon cycle
Super computer 2007
- 4th assessment of the IPCC
- interaction of vegetation
- feedback albedo
- atmospheric chemistry
