UNIB10007 Lecture Notes - Lecture 5: Representative Concentration Pathways, Sea Level Rise, Radiative Forcing
16 May 2018
School
Department
Course
Professor
TOPIC 5: FUTURE CLIMATE CHANGE
• GHG concentrations determined by economy + populations in the future
• 2 scenarios: also known as representative concentration pathways (RCP)
• Not much can be done to reduce sea level rise – up to 800 years for ocean to redistribute temperatures, last
time temp was 2-3 degrees above present, sea levels 25 metres higher
• IPCC:
o “Continued emissions of GHG will cause further warming + changes in all components of the
climate system. Limiting c.c will require substantial reductions of GHG emissions”
o “Changes in global water cycle in response to the warming over the 21st century will not be
uniform. Contrast in precip between wet + dry regions, and wet + dry regions will increase”
o “Global mean sea level rise will continue, very likely to exceed observed rises between 1971-
2010 due to ocean warming + increased loss of mass from glacier + ice sheets”
o “Cumulative emissions of CO2 largely determine global mean surface warming – most aspects
of c.c will persist for many centuries even is CO2 emissions are stopped”
High GHG Emission Scenario
Rapid Emission Reduction Scenario
• From 2 watts/square metre to 8 by end of century
(direct radiative forcing change)
• CO2 ppm increases to 1,000, radiative forcing up to
1,300
• Temperatures increase 4.6 degrees from pre-industrial
levels, temps never experienced by homo-sapiens
• High + low latitudes, + tropics = consistent precip
increase
• High pressure belt, already dry regions = getting drier
• Increased rise in sea level
• Peaks at 3 w/square metre, then
reduce
• C02ppm peaks, then reduces to
just above 400ppm
• Temps increase 1.6 degrees from
pre-industrial levels
• Even in this scenario, 20%
chance of warming more than 2
degrees
• Less changes in precipitation
• Rise in sea level, to lesser extent
Projected Changes
• Certain: more frequent hot + fewer cold temp extremes over most land areas on daily + seasonal timescales
as global mean temp increases
• Extreme precip events over most of mid-lat land masses + wet tropical regions – more frequent + extreme
as mean surface temp increases
• 100-year time scale: all CO2 released will still have warming effect on planet, even if CO2 is stopped
today, lag effect = ocean + land will continue to warm
• Linear relationship between cumulative effects of CO2 + temperature change
Carbon Budget: global measure of cumulative amount of CO2 consistent with avoiding temp increase of over
2 degrees
• For this to occur, 80% of under-the-ground fossil fuels needs to remain un-used
Projected Climate Change in Australia in 2050
• All areas will increase in temperature, by a minimum of 1.5 degrees
• Rainfall decreases in majority of areas, stable in tropics, all other places see declines in precipitation
• Melbourne:
o Low Emissions: 1.4 degrees, -2% (sum), -7% (winter) rainfall. -10% rainy days, 14 days above
35 degrees
o High Emissions: 2.8 degrees, -4% (sum) -12% (winter) rainfall, -19% rainy days, 20 days above
35
TOPIC 6: IMPACTS OF CLIMATE CHANGE
• How are risks assessed? How do you compare benefits + detriments?
• Already widespread observed impacts of c.c in natural + human systems
Document Summary
Ipcc: continued emissions of ghg will cause further warming + changes in all components of the climate system. Limiting c. c will require substantial reductions of ghg emissions : changes in global water cycle in response to the warming over the 21st century will not be uniform. Contrast in precip between wet + dry regions, and wet + dry regions will increase : global mean sea level rise will continue, very likely to exceed observed rises between 1971- High ghg emission scenario: from 2 watts/square metre to 8 by end of century. Rapid emission reduction scenario: peaks at 3 w/square metre, then (direct radiative forcing change) reduce, co2 ppm increases to 1,000, radiative forcing up to, c02ppm peaks, then reduces to. Increased rise in sea level chance of warming more than 2 degrees: less changes in precipitation, rise in sea level, to lesser extent. Carbon budget: global measure of cumulative amount of co2 consistent with avoiding temp increase of over.
