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.

Aerosols

When we talk about aerosols, we mean solid particles and liquid droplets that can be found in the air over oceans, deserts, mountains, forests, ice and every ecosystem in between. There are many different ways of classifying aerosols, but climatologists use the chemical composition, so we can find the following groups: sulphates, organic carbon, black carbon, nitrates, mineral dust, and sea salt. In practice, many of these terms are imperfect, as aerosols often form complex mixtures.

The main part of aerosols, about 90 percent by mass, has natural origins. For instance, volcanoes eject columns of ash into the air, as well as sulfur dioxide and other gases.  Another example is the ocean, some microalgae produce dimethylsulfide which converses into sulfates in the atmosphere. Sea salt and dust are two of the most abundant aerosols.

The remaining 10 percent are considered anthropogenic  and they have many sources including, fossil fuel combustion and biomass burning, among others.

Aerosols and incoming sunlight – direct effects

Aerosols reflect a quarter of the Sun’s energy back to space. Different aerosols scatter or absorb sunlight in different degrees, depending on their physical properties; and this is a direct effect of aerosols on the Earth’s radiation field.

On one hand, pure sulphates and nitrates reflect nearly all radiation they encounter, cooling the atmosphere. On the other hand, Black carbon absorbs radiation, warming the atmosphere and the surface.

Volcanoes eruptions eject large amount of sulphur dioxide to the atmosphere. As a result of the global sulfate infusion, global temperatures drop.

In addition to scattering or absorbing radiation, they can alter the albedo of the planet. Bright surfaces reflect radiation and cool the climate, whereas darker surfaces absorb radiation and produce a warming effect.

Aerosols and clouds – indirect effects

On a global scale, the aerosols can form clouds that cause cooling. Those clouds are bright, it means that they will scatter more light and become more reflective; blocking the sunlight from reaching Earth’s surface and producing a net cooling. The “cloud albedo effect”, as we know this cloud brightening effect, make a significant impact on the climate.

Current estimates suggest the cooling driven by aerosol indirect effects is less than half as much as the warming caused by greenhouse gases when average over the globe. But if we consider a smaller space and time scale, the climate effects of aerosols can be significant.  

For further information on aerosols, visit the following link: 

NASA Earth observatory – Aerosols http://earthobservatory.nasa.gov/Features/Aerosols/

This explanation about the aerosols and its interaction with the climate, including the direct and the indirect effects are part of the exercises on a Future Learn course on Climate Change by the University of Exeter.

Climate change records

In order to understand the world’s climate and how it has changed through centuries, we need long-term worldwide observations of the atmosphere, oceans and lands surface. But we have a lack of information, some of the problems related with it, are exposed below:

Geographical coverage and gaps in the historical record

The main obstacle in assessing past climate change has been the fact that a lot of observations aren’t complete. Climate observations were mainly limited to weather stations and vessels, and only included measurements made at or near the land or the ocean surface. In the 19^th century, many parts of the world were not monitorated at all. In the last years this have changed,

•       Since the 1950’s weather balloon sounding have been widespread over land.
•       Satellites are used for monitoring the climate; it gives us a worldwide coverage since 1970s. The measures include Sea surface temperature (SST), Sea Ice extension, Chlorophyll, etc.  
•       More than 3611 free-drifting profiling floats that measures the temperature and the salinity of the upper 2000m of the ocean in the Argo project. This allows, for the first time, continuous monitoring of the temperature, salinity, and velocity of the upper ocean, with all the data transferred and published in a global platform.

Profiling float, Argo project - Malaspina Leg 3 Indian Ocean

For the last two centuries, the scientists have improved the availability of instrumental data. Many data was only available from paper logbooks, some of these data has been put in computer databases. Nowadays, most data collected is recorded on databases. 

Using indirect or proxy measurements 

Before 1600’s we don’t have direct measurements of changes in climate, so scientists have used indirect or proxy methods, such as,

•        Tree-ring and ice-cores for inferring changes in temperature and precipitation.
•        Depth profiles of temperature in oil-drilling boreholes to estimate the changes in air temperature.
•        Corals to estimate the ocean temperature and the sea-level changes.

These indirect or proxy methods are not as precise as direct instrument measurements, however, long-term temperatures trends confirms climate in the past two thousand years was no as warm as it has been in recent decades.

Varying standards for taking observations

When we are comparing data from different sources, we have to take into account that the different measurements have been taken with different methods and that those methods have changed through the time. That’s the reason why International standards have been developed for observing practices. Those standards, for both satellite and ground-based data, include the requirement to overlap records in order to have more reliable information. 

Useful links:

Argo information centre - http://wo.jcommops.org/cgi-bin/WebObjects/Argo

Argo steering team - http://www.argo.ucsd.edu/

Argo  - España - http://www.oceanografia.es/argo/

Met Office - Climate change and observations

http://www.metoffice.gov.uk/climate-change/guide/science/explained/observations

NOAA Ocean Products – Environmental Satellite data and information service http://www.ospo.noaa.gov/Products/ocean/index.html

The climate system

Last week I started a MOOC course on climate change at Exeter University, as the final exercise of the first unit, we were asked about some reflections on the topics we have learned.

We can understand the climate as a system where different components: Atmosphere, Hydrosphere, Biosphere, Cryosphere and Lithosphere, interact. There are a wide range of natural cycles, but the water cycle is the one which illustrates better the climate system. Solar radiation causes the evaporation of the water from lakes, rivers and oceans (hydrosphere). and also water evaporation and transpiration from green plants (biosphere). The water vapor condenses in the atmosphere forming clouds and then it returns to the surface through precipitation as rain and snowfall. When reaches the surface, water returns either to the hydrosphere or to the cryosphere, if it is frozen snow. Sunlight can melt snow and ice or transform it into vapor from the ice sheets, snow fields and glaciers, by sublimation. All those processes are influenced by many factors including human activities.

When we consider the dynamics of our climate system, we’re not just talking about simple cause and effect. The cycles that connect components of the climate system create feedback loops, as well; closed loops of cause and effect. Here the three key feedbacks that play an important role in our climate system: Water vapor feedback, ice albedo feedback, and the radiation feedback.

1.       Water vapor feedback: As the evaporation increases, more water vapor on the atmosphere and a increase of temperature, that helps the evaporation, and so on. This is a positive feedback.  

2.       Albedo feedback: The sea ice has a high albedo but the ocean has a low albedo. The radiation arrives at the ocean and it is absorbed. The sea ice melts, and produces an increase on the ocean water. Then the albedo of the sea ice decreases and so the reflection, increasing the absorption of the sea. This warming on the ocean will melt more sea ice, and so on. This is another positive feedback.   

3.       Radiation feedback: Stefan Boltzmann effect or Planck feedback. All the objects give off radiation, and when this happens, the object cools it down. This is an example of negative feedback.

Thanks to the different positive and negative feedbacks this systeself-regulates itself. 

Useful links:
·        NOAA - Climate http://www.climate.gov/
·    Professor Tim Lenton's Climate Change MOOC blog - http://blogs.exeter.ac.uk/climatechangemooc/

About this blog

I’m an oceanographer interested in learning and discovering the world. For the last ten years I’ve lived in different places, met interesting people and built myself, through all the experiences I’ve lived.

Maybe it’s time to record all those things in one place. It’s time to share all those thoughts, reflections and memories.