L8 - The Hockey Stick Flashcards
What 3 things need to be considered for climate change over the past millennium?
- Are there similarities across the globe?
- Is there evidence for millennial and orbital variability?
- Is 20th century warming due to natural or anthropogenic causes?
When was the little ice age and how much cooling was there?
1500s/1600s
0.5 Deg C
What 2 changes have there been in the last century?
- Global retreat of glaciers
2. The Hockey Stick!
What are the 5 main archives for looking at climate change in the last 1000 years?
- Polar Ice Cores
- Mountain Ice Cores
- Tree Ring Records
- Corals
- Marine Sediments
Give 5 pre-industrial records
- Anecdotal written accounts
- Ships Log
- Drawings
- Photographs
- Written descriptions
Give 5 problems with instrumentation that aren’t climatic influences
- Changes in instrument station location
- Changes in observation times
- Changes in instrumentation
- Changes in the observation environment
- Calibration Requirements
When were mercury thermometers invented?
17th C
When did the temperature record in Central England begin?
1659
Since when has there been unprecedented warming?
1980
What was the warmest year on record with respect to the the 20C averages?
2015
What 2 things do SL measurements have to corrected for?
- Isostatic Uplift
2. Tectonic Uplift
What are the 2 main contributors to SLR?
- Thermal Expansion
2. Glacier/Ice Sheet Melt
What is happening to sea ice?
General Trend of Reduction in the Northern Hemisphere
Have modern instruments indicted that there is a global trends of anomalous conditions (the hockey stick)?
Yes
How much cooling have orbital variations caused in the North in the last 1000 years?
~0.2 Deg C
What can orbital timescales not be used to explain?
The unprecedented warming
What can decadal to century timescales be used to explain?
Variations on weekly, monthly and yearly timescales
What are annular modes?
Changes in the N/S shift of the atmospheric masses between the polar regions and the mid latitudes
What is NAM and its other 2 names?
Northern Annular Mode AKA Arctic Oscillation or North Atlantic Oscillation
What is SAM and its other name?
Southern Annular Mode AKA the Antarctic Oscillation
What is the NAO?
North Atlantic Oscillation – variations in atmospheric pressure between Iceland and the Azores (no distinct periodicity)
What happens when the NAO is in +ve mode?
High pressure over the Azores, warmer conditions and wetter in the North
What happens when the NAO is in -ve mode?
Decreased pressure difference, polar winds and wetter conditions in the Mediterranean
What has happened to the NADW in the last 40 years and what is a possible explanation for this?
Rapid freshening – the NAO could be in +ve mode causing increased pptn in the Nordic Seas = more freshwater
What can periods of solar minima/blocking cause? and when was this thought to be the case?
- ve NAO (fresh and cold conditions)
e. g. Maunder Minimum during the Little Ice Age
Long term, what does increased volcanism cause?
Increased CO2
What impact does aerosols have on volcanism?
There are cooling events such as after Mount Pinatubo in 1991
Following the eruption of Mount Pinatubo in 1991 what was the immediate and longer term cooling?
~0.6 Deg C in the immediate Summer and ~0.3 Deg C in the years after until noise meant that the effect was lost
How often does El Niño occur?
Every 2-7 years
During an El Niño year how much warming is there globally?
~0.1 Deg C
Can El Niño explain the overall trend of warming?
No
What happens in an La Niña year?
Low pressure in AUS and warm waters
Cold upwelling and High pressure in S.America
What happens in an El Niño year?
Drought in AUS
Flooding and decreased upwelling with 1.5 Deg C warming in S.America
What level is CO2 at today and what are the 2 main reasons for this?
> 400ppm
- Land Clearance
- Fossil Fuels
How much more powerful is methane than CO2 but why is not having as much of an impact?
20x more but less concentrated/lower amounts of it
What % of methane comes from natural and anthropogenic sources?
70% - anthropogenic
30% - natural
What did the AOGCM modelling show?
That natural and anthropogenic forcing was needed to explain the global mean surface temperature anomalies in the hockey stick
Which IPCC report outlines the anthropogenic forcings and had headline statements addressing observed changes and causes for climate change?
AR5 (2013)
Cooling over the last millennium is caused by what?
Natural Causes
Warming over the last 200-250 years is caused by what?
Anthropogenic Causes
