Climate Change, Week 5

Over the past two decades scientists have recorded an alarming response to global warming in Greenland, ice loss has increased over time with glaciers showing an increase in flow speed and thinning.

I am currently studying an online course on Climate Change from the University of Exeter, facilitated by Future Learn. Future Learn offers a diverse selection of courses from leading universities and cultural institutions from around the world. These are delivered one step at a time, and are accessible on mobile, tablet and desktop, so you can fit learning around your life. Oh and did I mention it is completely free? I recommend them, if you have a thirst for learning, you should check them out.

Key Lessons

Based on the end of week quiz (result was 15 out of 15, or 100%).

  1. Melting sea ice has no effect on sea levels, however it does amplify warming in the Arctic due to exposed sea water absorbing more solar radiation. It also reduces polar bear hunting grounds.
  2. Carbon dioxide reacts with water to form carbonic acid, an unstable compound which quickly dissociates into bicarbonate ions and hydrogen ions.
  3. Since the Industrial Revolution the world’s oceans have dropped by a 0.1pH unit. If we continue to burn fossil fuels as expected and atmospheric carbon dioxide levels increase, it is predicted that the pH of the oceans will fall another 0.3 to 0.4 pH units.
  4. The Antarctic and Greenland ice sheets contain more than 99% of the glacier ice on Earth, this is the equivalent of around 65 meters of sea level potential.
  5. Ice geometry (thickness, steepness), ice properties (temperature, density), terminal environment (land, sea, ice shelf, sea ice) and mass balance (rate of accumulation and ablation) all control the process of ice flow.

The Cryosphere

The cryosphere describes all of the ice on the planet, so things such as glaciers and the ice caps, it is a critical component of the climate system. As the planet warms, sea levels will rise. The current contribution to sea level rise is mostly from thermal expansion of the oceans and melt from mountain glaciers.

However there is a far more dangerous source of sea level rise which is constantly under threat, that may be nearing a tipping point whereby the damage can not be undone. Ice sheets across Antarctica and Greenland make up 99% of the glacier ice on Earth, there is the equivalent of 65 meters of sea level rise locked in through those ice sheets.

Over the past two decades scientists have recorded an alarming response to global warming in Greenland, ice loss has increased over time with glaciers showing an increase in flow speed and thinning. Half of the total mass loss of ice is from surface melt, whilst the remainder is due to blocks of ice breaking off, forming icebergs where the glacier meets the sea. This process is known as calving.

Ice sheets spread out under their own weight. As it snows more, the pile will get larger, resulting in a positive mass balance. If the melt rate increases, and it’s larger than the amount of snowfall, a negative mass balance will present, resulting in the pile getting smaller.

Much of the increase in mass loss from Greenland has resulted in an increase in ice flow or spreading. Basil lubrication occurs when surface meltwater drains to the bed, which helps the glaciers to move faster. Melt water which doesn’t drain to the bed or margins can collect on the surface to form lakes of up to nine square kilometres in size. These lakes have a lower albedo than the surrounding ice, so they absorb more solar radiation and warm the surrounding area. This can cause lakes to drain suddenly, sending a substantial amount of meltwater through the ice sheet to the bed, increasing the amount of basil lubrication. The warmer meltwater can also transport heat into the interior of the ice sheet, causing the ice to soften and deform in order to flow faster.

Ocean Acidification

Oceans cover 70% of Earth’s surface, and owing to the fact they are so deep, they contain 99% of the living space for animals on our planet. They are responsible for a large proportion of global biodiversity, with around 250,000 species of animals living in the ocean that we currently know of. Around a third of the oxygen we breathe is produced by phytoplankton living in oceans, this, along with the fact that much of the world relies on oceans as a source of food, means that the oceans health has a direct link to our health. Personally speaking, as a vegan, I don’t believe we should be relying on the oceans to source our food (with the exception of seaweeds).

Ocean Acidification is caused by raising levels of carbon dioxide in the atmosphere. Carbon dioxide is soluble in sea water, absorbing about a third of the carbon in the atmosphere. As it dissolves, it mixes with the sea water to form carbonic acid. This carbonic acid is unstable, and quickly dissociates into two irons, bicarbonate, and hydrogen ions.

The concentration of hydrogen ions in seawater determines its pH, at the moment, the pH of seawater is approximately 8.1. Naturally, as the carbon dioxide levels in the atmosphere increase, so does the amount of bicarbonate and hydrogen ions in seawater.

The ocean has a natural buffering system known as the carbonate buffer, carbonate ions in seawater soak up hydrogen ions, taking them out of the ocean acidification process. It’s this process that has kept the pH of the ocean stable for millions of years. Carbonate ions enter seawater through natural weathering of rocks, such as limestone, and also from the shells of dead marine animals. These are very slow processes, ocean acidification is happening because the rate at which we put carbon dioxide into the atmosphere is greater than the rate at which carbonate ions are being put into the ocean. With less carbonate ions available to soak up the hydrogen ions, the oceans pH is beginning to fall.

Since the industrial revolution, the pH of the ocean has fallen by 0.1 of a pH unit, which is the equivalent of a 30% increase in hydrogen ions in the seawater. This is naturally causing difficulties for many species living in the oceans. If we continue to release carbon dioxide into our atmospheres, at the rates currently predicted, by 2100 there will be a 120% increase in hydrogen in the oceans. This will have catastrophic effects.

Ocean Acidification and Marine Invertebrates

Marine invertebrates make up the largest proportion of the oceans biodiversity, with up to 76% of marine animals being invertebrate species. These include crabs, sea urchins, limpets and snails. These species are crucial to the oceans, as they are bottom of the food chain animals (poor invertebrates!). So when these species start to disappear, so to will the larger animals such as the fish we eat. The biggest threat to marine invertebrates, is ocean acidification.

A large number of marine invertebrates have calcium carbonate shells or skeletons. Calcification is the precipitation of calcium and carbonate ions which form a solid shell. Once the shell has been formed, the calcium carbonate structure is vulnerable to dissolution again, unless it is surrounded by seawater that has saturated calcium carbonate levels in it. If the surrounding seawater becomes under saturated with carbonate ions, these structures begin to dissolve. As ocean acidification progresses, the amount of carbonate that is available for these shells to form and remain healthy will start to decrease, resulting in the loss of millions of animals across the world. As these creatures are important to the food chain, this will have a direct effect on countless other species, and one of man kinds most abundant sources of food.

Further Reading

Greenland Ice Sheet Surface Conditions (Polar Portal)

Marine Ice Sheet Instability (Antarctic Glaciers)

Ocean Acidification (OCB)

Global Challenge of Ocean Acidification (NRDC)

Climate Change and the Oceans (NASA)