Changes to the Cryosphere
Ice loss from the ice cap
Sea Ice is frozen salt water, changes to sea ice cover don't impact on sea levels. While the volume of water increases on freezing, the amount of water it displaces is unchanged.
It's ice from the massive ice sheets, accumulated snow lying several kilometers thick over Greenland and the Antarctic that cause sea level rises. Ice from the ice cap is made of fresh water and it affects sea levels in two ways.
One is calving icebergs. When glaciers reach the shore they push ice on to the surface of the water that eventually breaks up into icebergs. An easy way of seeing the difference between sea ice and glacial ice is is to make a Gin and Tonic with an ice cube in it representing the sea ice. Mark the level of the liquid then let the ice cube melt -levels will remain the same. Now add a few more ice cubes - that's a glacier calving.
The delicious cocktail will have been displaced up the glass - a fair analogy of the impact of calving icebergs. Always remember to drink the G&T as soon as the experiment is concluded or the melting ice will spoil the drink. It is important to replicate experiments in science so this is a really useful way of expanding knowledge and having a fun evening.
The other is melt water runoff. If summer melt and winter rain are in equilibrium this process will not affect sea levels - but if summer melt exceeds precipitation there will be an overall decrease in ice mass and an increase in sea levels.
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| Summer meltwater cascading into a sink hole |
There are some interesting images of the retreat of glacial outlets on the Polar Portal web site, showing images from the 1980's and today.
Their data shows that the total loss of mass from the ice sheet since 1840 equates to a 25 mm addition to global sea level . It also shows mass loss has accelerated over the last few decades - with the largest ice loss rates since 1840 occurred in the most recent decade and the mass loss in 2012 setting a new record.
Satellite measurements showing chilling figures for ice mass loss in Greenland:
- in the period 1992-2000 the ice sheet lost 51 Gigatonnes per year, adding 1.4 mm to global sea level per decade.
- From 2005-2010 263 Gigatonnes per year were lost - equivalent to 0.73 mm per year of sea level rise
- From 2008-2012 the average annual mass loss has increased to 367 Gt (1.0 mm sea level rise per year).
A increase in sea level rises from 1.4 mms in a decade to 10 mms in a decade is alarming - but there are fears that under certain conditions both the Greenland and the West Arctic Ice sheet could destabilise even more rapidly. If a tipping point were reached the West Antarctic Ice Sheet it could add over 3 metres to sea levels in the course of a couple of centuries.
The diagram offers an explanation of how ice sheets may destabilise more rapidly than expected
Ice loss from the sea
The loss of sea ice presents a separate set of issues. Summer cover has declined dramatically over the last 30 years. This US National Oceanic and Atmosphere Administration video shows record breaking ice loss in the year 2012
The loss of sea ice is probably having a far more immediate impact than the loss of ice cap mass. It directly affects both native wildlife and human Arctic populations, which are also subject to other impacts from climate change, described in detail in the newly published Arctic Biodiversity Assessment.
It's retreat is reducing albedo, creating positive warming feedbacks as the darker exposed seas absorb heat and it's highly probable that loss of sea ice is impacting on our climate. Even worse - recent studies indicate that the impact of sea ice loss on warming may be far more severe than previously feared, with the US government's National Oceanic and Atmospheric Administration predicting warming by as much as 13oC if CO2 is not mitigated
This Jeff Masters Blog goes into detail about the way sea ice loss contributes to increased warming in the polar regions, which in turn can displace the jet stream - driving Atlantic lows and very cold Arctic air masses further south than in the past. This 15/02/2014 news report from the BBC explains how these changes could be contributing to the recent severe weather being experienced in Europe and in the USA.
Ice loss in the mountains
The cyrosphere embraces high altitudes as well as high latitudes and another indication of climate change is the loss of mountain glaciers. Stunning images in the Himalayas show the mountains today shot from the same positions as their earliest known images - some going back as far as the 19th C. At first glance it would seem the retreat of mountain glaciers, though another indicator of warming, is less of a concern than loss of sea ice and mass from ice caps - but glaciers form an important source of water for some of the world's great rivers - including rivers flowing into the Indian subcontinent that provide water for over a billion people.
There are similar concerns in the USA where the Rockies have seen a 20% loss of ice cover in the last 3 decades - Runoff from the Rocky Mountain snows accounts for 60 to 80% of the annual water supply for more than 70 million people in the western US. The timing of snowmelt affects the levels of water available for crop irrigation and hydro-electric power (reported in countercurrents blog)
It seems that although, rising sea levels, the "traditional" fears of polar warming, are happening, it will be some time before the impacts really begin to be felt. The loss of sea ice appears to be having a mre immediate disruptive effect on our climate and may well be the underlying cause of the severe weather experienced in the UK this year, while ice loss from the mountains has the potential to affect the water supply of billions of people.
As if this isn't bad enough, warming at the poles raises the spectre of another amplifying feedback being set in motion, Permafrost holds a vast store of carbon locked into semi decomposed vegetation and deposits of methane clathrates lie on the sea bed in cold Arctic waters. As the polar regions warm methane - a 30 times more powerful greenhouse gas than CO2 - will be released in as yet unknown quantities.
Marine Acidification
"Oceans cover 70% of the planet's surface, because they're deep, they actually contain 99% of the living space for animals on our planet. So they contain a large proportion of global biodiversity"
(Dr Ceri Lewis- Futurelearn video)
(Dr Ceri Lewis- Futurelearn video)
I've been aware of the issue for a while but hadn't quite appreciated the fact that it represented so much of the world's inhabitable space, and it makes the story of rising acidity in the sea, the "hidden side" of carbon pollution, even more daunting.
The sea is the main reasons why atmospheric CO2 concentrations have not risen proportionately to emissions. Carbon Dioxide is soluble in water, forming Carbonic Acid - and around about a third of all anthropogenic emissions have been absorbed by the sea. In terms of ppm of CO2 this is a good thing - but the increased acidity of the sea has potentially profound implications for the future of 250,000 plus marine species.
I'm not going to go into the detail of the chemistry - there's a really good account of this in the Ocean Acidification Wiki. It's enough to know that dissolved CO2 has caused an increase in the sea's acidity of around 30% since 1750.
This is a serious cause for concern as many marine species form calcium carbonate shells that can become soluble in acid conditions. There's a quick guide to some of the ramifications of rising acidity from the Marine conservation and Biology Institute here. Effects include the obvious like coral bleaching and dieback, but it's perhaps the effects at the tiniest level that are most worrying.
The majority of marine life reproduce by releasing eggs and sperm into the water - to form embryonic versions of their parents. These are incredibly sensitive to acidity - and as part of their development, many need to form lime shells or skeletal structure. Clearly an acid environment compromises their development. The effects on plankton are an even greater worry . Plankton are at the base of the marine food chain and help produce a third of the world's oxygen supply.
A quick trawl through google asking the question, "effects of marine acidification on phytoplankton?" comes up with a host of links" - none of them very positive. These examplesgive a flavour of the kind of issues acidification will create:
I want to share this link too - it's a great resource for teachers and the site goes into detail on many other climate change issues too
I was very stimulated by the discussion thread this week. I've really noticed that most comments tend to interpret the problems of climate change in human terms.
I tend think in terms of "catastrophic loss of biodiversity - we are part of a system and, in biological terms , not a particularly important part at that, just numerous. I'm inclined to feel marine acidification is a far greater threat to the complex system that maintains our current biosphere than rising sea levels - which will just make life difficult for humans.
Acidity is rising most rapidly in the polar regions nutrient rich seas. The phytoplankton that bloom in these waters each year are at the base of the marine food chain - with hundreds of larger life forms depending on them for survival. Phytoplankton's are also a major contributor to the third of the world's oxygen that comes from our oceans. Phytoplankton is potentially very vulnerable to rapid pH changes. Potentially, this could pose huge problems for the entire marine ecosystem. It's too soon to say exactly how marine acidification will affect the sea but it's highly probably it will be a big big problem, because, in terms of pH, the damage has already been done, and can't be stopped.
A number of people were saying "it will be OK" or offering opinion along the line of, "well - marine organisms can migrate to less acid, more suitable areas". I try not to let it happen, but the phrase "is it me" occassionally springs to mind unbidden. Anyone following that line of reasoning might just reflect that a lot of marine life is sessile and exist in specific depth ranges, so can't cross deep oceans. A lot of species can only survive in specific temperature ranges and many mobile species depend on a community of non-mobile organisms to provide a suitable habitat. Oh - and eventually sea water mixes - so higher acidity will be universal.
We were asked this week - what did we think posed a bigger threat to humanity, sea level rise or marine acidification - personally I find marine acidification far scarier than global warming in it's entirety. Sea Level rises we can survive - but acidification is utterly unquantifiable. I try and avoid Armageddon scenarios - but at it's worse - if acidification causes massive disruption to the marine eco-system, I believe we could be looking at such profound changes to the earth's global environment, that life as we know it could be largely wiped out. I've stared climate change in the face for 30 odd years and always tried to remain positive - marine acidification terrifies me.
This is a serious cause for concern as many marine species form calcium carbonate shells that can become soluble in acid conditions. There's a quick guide to some of the ramifications of rising acidity from the Marine conservation and Biology Institute here. Effects include the obvious like coral bleaching and dieback, but it's perhaps the effects at the tiniest level that are most worrying.
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| Rockpool in Brittany - 10 different large marine species in this image |
A quick trawl through google asking the question, "effects of marine acidification on phytoplankton?" comes up with a host of links" - none of them very positive. These examplesgive a flavour of the kind of issues acidification will create:
- Study suggesting that increased acidity would favour smaller species to the detriment of larger plankton species, important in both carbon sequestration and the release of gasses that give clouds higher albedo -
- Italian study carried out in water made acid by volcanic co2 emissions shows low species diversity-
- US Geological Survey study showing rate of acidification in polar waters is increasing far more rapidly than expected
I want to share this link too - it's a great resource for teachers and the site goes into detail on many other climate change issues too
Reflections
I was very stimulated by the discussion thread this week. I've really noticed that most comments tend to interpret the problems of climate change in human terms.
I tend think in terms of "catastrophic loss of biodiversity - we are part of a system and, in biological terms , not a particularly important part at that, just numerous. I'm inclined to feel marine acidification is a far greater threat to the complex system that maintains our current biosphere than rising sea levels - which will just make life difficult for humans.
Acidity is rising most rapidly in the polar regions nutrient rich seas. The phytoplankton that bloom in these waters each year are at the base of the marine food chain - with hundreds of larger life forms depending on them for survival. Phytoplankton's are also a major contributor to the third of the world's oxygen that comes from our oceans. Phytoplankton is potentially very vulnerable to rapid pH changes. Potentially, this could pose huge problems for the entire marine ecosystem. It's too soon to say exactly how marine acidification will affect the sea but it's highly probably it will be a big big problem, because, in terms of pH, the damage has already been done, and can't be stopped.
A number of people were saying "it will be OK" or offering opinion along the line of, "well - marine organisms can migrate to less acid, more suitable areas". I try not to let it happen, but the phrase "is it me" occassionally springs to mind unbidden. Anyone following that line of reasoning might just reflect that a lot of marine life is sessile and exist in specific depth ranges, so can't cross deep oceans. A lot of species can only survive in specific temperature ranges and many mobile species depend on a community of non-mobile organisms to provide a suitable habitat. Oh - and eventually sea water mixes - so higher acidity will be universal.
We were asked this week - what did we think posed a bigger threat to humanity, sea level rise or marine acidification - personally I find marine acidification far scarier than global warming in it's entirety. Sea Level rises we can survive - but acidification is utterly unquantifiable. I try and avoid Armageddon scenarios - but at it's worse - if acidification causes massive disruption to the marine eco-system, I believe we could be looking at such profound changes to the earth's global environment, that life as we know it could be largely wiped out. I've stared climate change in the face for 30 odd years and always tried to remain positive - marine acidification terrifies me.
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