Thursday, 30 January 2014
Week 2: 400 parts per million
Understanding past climate changes can be key to understanding the state of the climate in the future. On May 9, 2013, carbon dioxide levels in the atmosphere reached the level of 400 parts per million (ppm). The last time the Earth experienced this level of carbon dioxide was in the Pliocene about three to five million years ago.
In the mid-Pliocene average global temperatures were 2-3 deg C higher than today, and sea levels were 25 to 30 metres higher than today.Cooling and drying occurred in the late Pliocene. These changes were likely caused by reducing levels of CO2 in the atmosphere due to increased chemical weathering (many mountain ranges uplifted in this period), increasing ice at high latitudes giving increased albedo, and possibly reduced solar insolation.
The data on CO2 concentrations demonstrate a clear correspondence between the Pliocene climate (due to natural causes) and the contemporary climate conditions (caused by anthropogenic actions). What really worries scientists about our contemporary CO2 concentrations is the breakneck speed at which they are increasing.
In the mid-Pliocene average global temperatures were 2-3 deg C higher than today, and sea levels were 25 to 30 metres higher than today.Cooling and drying occurred in the late Pliocene. These changes were likely caused by reducing levels of CO2 in the atmosphere due to increased chemical weathering (many mountain ranges uplifted in this period), increasing ice at high latitudes giving increased albedo, and possibly reduced solar insolation.
The data on CO2 concentrations demonstrate a clear correspondence between the Pliocene climate (due to natural causes) and the contemporary climate conditions (caused by anthropogenic actions). What really worries scientists about our contemporary CO2 concentrations is the breakneck speed at which they are increasing.
Week 2: Recommended readind
What are climate change records?
Climate change records are vital in understanding our climate; in the past, in the present and in the future.
We observing the climate their are many challenges such as incomplete geoghrapical coverage of measurements, gaps in historical climate records, the need to use some indirect measurements of climate change, ciases and errors in data, varying standards for taking observations, collecting information to assist interpretation of climate records, calculating changes in climate and estimating incertainties in climate observations.
We need long-term worldwide observations of the atmosphere, oceans and land surface to understand the world's climate and how it has changed. Climate chnage records are many diffrent ways of knowing how our climate has changed overtime.
A major obstacle in assessing past climate change has been the fact that a lot of observations aren't complete. Before the 1950s, climate observations were mainly limited to weather stations and ships, and only included measurements made at or near the land or ocean surface. In the 19th century, many parts of the world were not monitored at all. There are few complete daily instrumental records stretching as far back as the eighteenth century.
As there are no records of climate from direct measurements before the 1600s, scientists have used other types of information to investigate further back such as tree-rings and ice-cores can be used to infer changes in temperature and precipitation, depth profiles of temperature in oil-drilling boreholes can be used to estimate the changes in air temperature over recent centuries and corals can be used to estimate oceanic temperature and sea-level changes.
How do volcanoes affect climate change?
How is today’s warming different from the past?
What is the role of isotopes in determining temperatures from the past?
How have trees been used to reconstruct different climate variables across the world?
How can ice cores provide a record of atmospheric composition?
Climate change records are vital in understanding our climate; in the past, in the present and in the future. We observing the climate their are many challenges such as incomplete geoghrapical coverage of measurements, gaps in historical climate records, the need to use some indirect measurements of climate change, ciases and errors in data, varying standards for taking observations, collecting information to assist interpretation of climate records, calculating changes in climate and estimating incertainties in climate observations.
We need long-term worldwide observations of the atmosphere, oceans and land surface to understand the world's climate and how it has changed. Climate chnage records are many diffrent ways of knowing how our climate has changed overtime.
A major obstacle in assessing past climate change has been the fact that a lot of observations aren't complete. Before the 1950s, climate observations were mainly limited to weather stations and ships, and only included measurements made at or near the land or ocean surface. In the 19th century, many parts of the world were not monitored at all. There are few complete daily instrumental records stretching as far back as the eighteenth century.
As there are no records of climate from direct measurements before the 1600s, scientists have used other types of information to investigate further back such as tree-rings and ice-cores can be used to infer changes in temperature and precipitation, depth profiles of temperature in oil-drilling boreholes can be used to estimate the changes in air temperature over recent centuries and corals can be used to estimate oceanic temperature and sea-level changes.
How do volcanoes affect climate change?
How is today’s warming different from the past?
What is the role of isotopes in determining temperatures from the past?
How have trees been used to reconstruct different climate variables across the world?
How can ice cores provide a record of atmospheric composition?
Wednesday, 29 January 2014
Week 1: Tim Lenton
Practice what you preach, as they say. So I have decided to do some reflective learning and blog about my experience with our Climate Change MOOC. It’s been great this week, seeing so much engagement with the course material on the discussion threads. But it left me looking for one place where I could respond to some of the issues that were catching fire, without having to repeat myself. Hopefully this will be it. So here goes with this week’s favourite topic – ozone…
Yes, we threw a curveball in the very first question on the course. A lot of people were surprised to hear that ozone (chemical formula O3) is a greenhouse gas, especially knowing that we have been trying to protect the ozone layer for the last twenty years. So, let’s tackle that one head on.
The first point to grasp is that ozone is present in two layers of our atmosphere – the well-mixed bottom layer that we breathe, known as the ‘troposphere’ – and the next layer up, known as the ‘stratosphere’ (because it is vertically stratified, i.e. layered).
It is in the stratosphere that the ozone layer forms, and it is the absorption of high energy (UV) sunlight by the ozone layer that heats up the stratosphere and gives it its stratification (with temperature increasing as a function of height).
Down in the troposphere ozone is a short-lived gas, concentrated near the surface, and produced as a by-product of chemical reactions acting on a range of mostly human pollutant gases, including oxides of nitrogen, carbon monoxide, methane, and other ‘volatile organic carbon’ species.
In both atmospheric layers, ozone functions as a ‘blanket gas’ absorbing heat radiation coming off the Earth and thus helping warm the surface. However, the warming associated with the stratospheric ozone layer is natural, and the ozone layer is doing a wonderful service shielding us from ultraviolet radiation, which we couldn’t live without. The ozone in the troposphere on the other hand has been increased in concentration by human activities, thus contributing to climate change – and it has some other nasty effects, like inhibiting plant productivity.
The depletion of the stratospheric ozone layer that was caused by human-produced chlorofluorocarbons (CFCs) did, as would be expected, tend to cool the planet, but only by a small amount when globally averaged. That cooling was more than outweighed by warming due to the CFCs themselves, which are potent ‘blanket gases’. And both effects are small compared to the contribution of carbon dioxide (CO2) to recent warming.
Interestingly, the creation of the ozone hole, as well as letting more UV radiation down to the Earth’s surface, has affected the climate regionally in Antarctica and the Southern Ocean, tending to keep things cool there, and leading to a strengthening of the winds encircling the planet above the Southern Ocean. Those strengthening winds have in turn tended to blow more sea-ice away from the areas where it is made around Antarctica, causing the surprising increase in area of Antarctic sea-ice that is so beloved of climate sceptics.
Hopefully that gives some glimpse of the beautiful, interconnected complexity of the climate system. Happily the stratospheric ozone layer is on the mend, but unfortunately the compounds we replaced CFCs with (the HCFCs) are still potent ‘blanket gases’. One day we’ll learn…
Professor Tim
Week 1: Intergovernmental Panel on Climate Change
http://www.ipcc.ch/publications_and_data/ar4/wg1/en/faq-1-1.html
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