Ocean acidification

In order to explain the ocean acidification, first we need to take a look on the carbonate system and how does it work in the ocean. As you can see from figure 1, CO₂ is exchanged between atmosphere and ocean from gaseous to aqueous form. The CO₂ dissolved, exists in three inorganic forms: as free carbon dioxide, CO₂ (aq.), as bicarbonate, HCO₃^-1, and as carbonate ion, CO₃^-2.

1. Carbonate system in the Ocean. Source: 2001, CO 2 IN SEAWATER:EQUILIBRIUM, KINETICS,ISOTOPES, Richard E. Zeebe and and Dieter Wolf-Gladrow, page 3.

 The relative proportions of CO₂, HCO₃^-1 and CO₃^-2 control the pH in the Seawater (see figure 2). At typical seawater conditions, bicarbonate is the dominant species, followed by carbonate ion, whereas dissolved dioxide is present only in small concentration. The pH of the seawater at the moment is about 8.1.

2. Carbonate system: Bjerrum plot, graphical representation of equilibrium relationships. The circle and the diamond indicate the constants of carbonic acid. Source: 2001, CO 2 IN SEAWATER:EQUILIBRIUM, KINETICS,ISOTOPES, Richard E. Zeebe and and Dieter Wolf-Gladrow, page 5. 

Typically, the ocean soaks up a third part of the atmospheric CO₂. However, these conditions are changing. The increasing CO₂ concentration in the atmosphere increases the amount of CO₂ that is being dissolved by the ocean, leading to a lower pH which means acidification of the ocean.

These changes in the equilibrium reduce the carbonate ion, CO₃^-2, which is the form of carbon that many organisms need to make shells and skeletons, coccolithophores, for instance. Ocean acidification is not only a problem for the animals which use carbonate in their skeletons and shells, but for the rest of them.

Some animals have a wide pH range of tolerance, for those animals will be easy to adapt to future changes on pH. But most of them have an optimum pH range which is quite limited, and a low tolerance to pH changes. If the pH falls below the tolerance range, that will lead to death due to respiratory or osmosis regulatory failure.

Sources:
2001, CO 2 IN SEAWATER:EQUILIBRIUM, KINETICS,ISOTOPES, Richard E. Zeebe and and Dieter Wolf-Gladrow
NASA Climate change - Ocean acidification  http://www.nasa.gov/topics/earth/features/climate_acidocean.html

Global Warming and Geo-engineering

When we talk about Global Warming we take a look on the Climate models. Those models assume different possible scenarios to predict future global warming, however it is difficult to estimate how much the greenhouse gas emissions will grow.

According to IPCC, the Earth will warm between two and sig degrees by 2100, depending on how fast carbon dioxide emissions grow (http://earthobservatory.nasa.gov/Features/GlobalWarming/images/ipcc_scenarios.png). Whereas the models that assume scenarios where people will burn more and more fossil fuel have the highest temperature rise; other scenarios assume a greenhouse gas emissions will grow slowly, giving lower temperature predictions.

Last IPCC report says Human activity has been the main cause of the observed warming since the mid-20^th century. Moreover, this influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, in global mean sea level rise, and in changes in some climate extremes.

Some scientists have been looking for solutions in order to modify Earth’s environment for controlling global warming and that is what we know as Geo-engineering. The Geo-engineering proposals include different ways to reduce temperature and CO2, cloud-whitening or ocean fertilization, for instance.

We need to assess the risks geo-engineering can cause to the Earth and its inhabitants since we don’t know for sure how the system will react to the proposed changes. The Ocean fertilisation could sink CO2 in the ocean floor, yet the CO2 biological and physical pump between the ocean and the atmosphere is very complex system (http://www.whoi.edu/cms/images/biological-pump_104615.png) and we don’t know how this system will change; so more research need to be done for understanding the implications of Ocean fertilization.

Would not be better to make more effort on reducing our CO2 emissions, rather than preventing the warming with geo-engineering? I definitely think so, we can try to fix the problems that we already have before we cause more troubles. 

Useful links: 
BBC News - Geo-engineering
http://news.bbc.co.uk/2/hi/technology/8338853.stm
http://www.bbc.co.uk/news/science-environment-19371833
IPCC - http://www.ipcc.ch/news_and_events/docs/ar5/ar5_wg1_headlines.pdf
NASA Earth observatory - Global warming http://earthobservatory.nasa.gov/Features/GlobalWarming/page5.php
WHOI - Ocean fertilisation http://www.whoi.edu/ocb-fert/page.do?pid=38315

Week 4 reflections on Climate Change course, University of Exeter. 

Extreme Events

If we take a look on the news, we will see examples of extreme events. All of us have seen those extremely low temperatures and huge snowfall storms along United States during the last month or, the bushfires that were burning for weeks in New South Wales, Australia, in October before the beginning of the warm season. 

Three sisters, Blue Mountains, New South Wales, picture taken in April, 2011. 

In order to explain Extreme events, I will use some figures from NOAA climate.gov.

Antarctica sea ice reached the highest extent ever recorded by satellites on September 26, 2012. The monthly average was a high record, as well, exceeding the previous record in 2006. Scientists believe that this can be explained by the stronger circumpolar winds in the Southern Hemisphere. These stronger winds push ice away from the coast, expanding the sea ice extend around many parts of the continent. 

Percent difference from average (1979-2000) sea ice concentration around Antarctica during January 2012 (summer minimum) and September 2012 (winter maximum).Dan Pisut, based on data from the National Snow and Ice Data Center.Source: Climate.gov - http://www.climate.gov/sites/default/files/bigJan_Sept_2013-IceAnom.jpg

If we take a look on Arctic sea, we have a completely different situation. On September 16, 2012, Arctic sea ice reached the lowest extent ever recorded.  

Ice concentration on September 16 compared to previous record low (yellow line) and the mid-September median extent (black line). Dan Pisut, NOAA EVL, based on datafrom the National Snow and Ice Data Center. Source: Climate.gov - http://www.climate.gov/sites/default/files/bigSeaIce-Sept162012.jpg

How can we explain those differences between the Poles?

The Antarctica is a continent covered by continental ice which has the Antarctic circumpolar current keeping the warm ocean waters away from the white continent. On the other hand, the Arctic Ocean is surrounded by continents and has a more complex circulation. We have water exchange in two main locations, the Bering Strait with the Bering Sea, Pacific Ocean; and between Greenland and Norway with the Atlantic Ocean. The wind patterns circulation is different for the Poles, as well.

As the Arctic warms, less reflection due to the sea ice melting, and having a temperature rise. 

If you want to learn more about Extreme Events on 2012, have a look on the following link: http://www.climate.gov/sites/default/files/bigextremes-201213_BAMSoriginal.jpg

Useful links:

NOAA - http://www.climate.gov/news-features/featured-images/state-climate-extreme-events

WHOI: Arctic Ocean Circulation - https://www.whoi.edu/main/topic/arctic-ocean-circulation

The Extreme Events in the Arctic and the Antarctica discussion belong to the Future Learn course on Climate Change by the University of Exeter.