Sea Level Lecture 6- Future Sea-Level Rise Flashcards
What is sea level inherently linked to?
Temperature
Will sea level rise likely continue for many centuries beyond 2100?
Yes, virtually certain global mean sea level rise will continue for many centuries beyond 2100- will continue no matter what we do today due to decisions we have already made.
Why will sea level continue to rise past 2100?
There are lags within the system – co2 stabilisation will take around 100 to 300 years, temperature stabilisation takes a few centuries, sea-level rise due to ice melting will take several millennia and sea-level rise due to thermal expansion will take centuries to millennia.
In terms of sea-level, what dominates the 20th century?
Thermal expansion and glacier melting dominate 20th century- around 75% of the observed rise since 1971.
Since early 1990s contribution of Greenland and Antarctica has increased.
Has land-water storage made a huge difference to sea-level?
A small but measurable difference
What are the IPCC emission scenarios?
Representative Concentration Pathways until 2100
Extension Concentration Pathways beyond 2100
What are the 4 IPCC scenarios?
2.6- low forcing (CO2 peaks and declines by 2100)
4.5- lower stabilisation scenario (CO2 stabilises by 2100)
6.0 higher stabilisation scenario (no peak in CO2 by 2100)
8.5- high greenhouse gas emissions (no peak in CO2 by 2100)
What happened to IPCC emission scenarios in AR6?
Added SSP (socioeconomic pathways)
What are the 5 SSPs?
1- sustainability
2- ‘middle of the road’ - world where trends follow broad historical patterns
3- Regional rivaly
4- Inequaity
5- fossil-fueled development
What year do IPCC scenarios start to look much more serious?
2050 outwards
What are methods of future projections of sea-level?
Aggregated vs disaggregated
Point estimate vs fully probabilistic
What are bottom-up scenarios?
Disaggregated and point estimate
Bring together all of the individual systems to feed into a sea-level prediction
Central range estimates: often the median, low and high quantiles
Have to incorporate processes we don’t understand well – issue within AR4
High end estimate: worst case scenarios- DeConto and Pollard (2016)
Probabilistic approaches: builds on the others.
What are probabilistic approaches?
Disaggregated and fully probabilistic
Takes information and for each piece of information give it a confidence level and work out what sea-level may be.
What are top-down scenarios?
Aggregated and point estimate
Focus on comprehensive metrics of change
Semi-empirical approaches
Expert judgement
What are high end estimates and bottum-up central ranges?
Disaggregated but halfway between point estimate and fully probabilistic
Discuss how sea level projections have changes through time.
First estimates of sea level projections were semi-empirical
Move towards fully probabilistic models in the last decade- better understanding and greater computational power.
What are semi-empirical models?
Aggregated and fully probabilistic
Look at relationships to predict aspect of model
Based on uncertainties and estimations
What are ‘expert elicitations’?
Aggregated and halfway between point estimate and fully probabilistic
People believed IPCC predictions were low
Asked many experts who believed it would be higher
How much was sea level projected to rise in AR4?
0.18-0.59 m
How much was sea level projected to rise in AR5?
0.26-0.82 m by 2100 but some suggest this may be too low
Why will sea level vary across the planet?
Many drivers of sea-level – will likely have some regional component. Will vary across the planet.
Is the idea of a global signal for sea level change meaningless?
Yes
What is UKCP18?
Fully disaggregated model, pull out different contributors.
Do projections of GMSL need to be made local to be useful?
Yes
