1. Modelling the climate system and climate change
RCM Workshop
Meteo Rwanda, Kigali
17thJuly 2017
This presentation is intended to provide an overall introduction. It won’t go into huge amounts of detail but should act as a signposting session to other talks later in the week.

2. Session contents Climate system interactions Climate variability
What is a climate model?
Projected climate change
These are the main areas that we will cover
Climate system interactions - Tom – What is the climate system,
how do the elements interact with each other?
Climate Variability – Hamish– What sort of changes have been happening in the climate. Where do they come from?
What is a climate model – Hamish – What is a climate model, how do they work? How have they changed over the years?
Projected Climate Change – Hamish – What do we think is going to change with the climate through the future?

3. Session Aims The goal of this session is to refresh your knowledge of:
the climate system
drivers of climate
climate variability
modelling the climate system
predicting future changes
By the end of the session you should have had an introduction to these

4. 1. Climate system interactions

5. What do we mean when we talk about climate?
Aim here is to get students to think about the difference between weather and climate.
Climate refers to a region’s long term weather patterns and is usually defined by statistics
(mean and variability) calculated over a 30 year period.

6. What do we mean when we talk about climate?
Climate refers to a region’s long term weather patterns and is usually defined by statistics (mean and variability) calculated over a specified time frame, such as 30 year period.
”annual average temperature across the Rwanda from ”
Aim here is to get students to think about the difference between weather and climate.
Climate refers to a region’s long term weather patterns and is usually defined by statistics
(mean and variability) calculated over a 30 year period.
WMO defines climate as over 30 years.

7. What is the Climate System?
The climate system is a complicated system consisting of various components, including the dynamics and composition of the atmosphere, the ocean, ice and snow cover, the land surface and its features, the many mutual interactions (i.e. feedbacks) between them, and the large variety of physical, chemical and biological processes taking place in and among these components.
Throw the question out to the room. If met with blank looks first get them to define climate.
Once we’ve got that, ask about the system.
Aim to encourage students to name some components of the climate system or some processes
and that these components and processes interact with each other

8. Exercise: work in pairs to fill in the blanks
At this point hand out the first exercise – students need to fill in the blanks using the words on the next slide and on the sheet.
Aim is to appreciate that the climate system is complex.

9. Hints: Wind stress Changes in the Atmosphere Land surface
Changes in the Ocean
Biosphere
Glacier
Changes in the Hydrological cycle
Ice – ocean coupling
Changes in Solar Inputs
Atmosphere-biosphere interaction
Soil-biosphere interaction
Rivers & Lakes
Evaporation
Land-atmosphere interaction
Changes in the Cryosphere
Atmosphere
Human influences
Volcanic activity
Changes in the land surface
Terrestrial radiation
Greenhouse gases & aerosols
Atmosphere – Ice interaction
Changes in the Hydrological Cycle
Clouds
Heat -exchange
Ice sheet
Ocean
Sea ice

10. Components of the climate system (answer)
This diagram combines the components just mentioned (e.g. atmosphere, land surface, ocean, biosphere) and indicates some points of interaction.
Do a simple example.. How does changes in the land surface affect the climate. A through albedo affecting energy received from sun.
We’ll focus on forcing and feedbacks in the next section.

11. Climate Forcing
Can be defined as an imposed perturbation on the Earth’s energy balance
For example - a change in solar irradiance, or a change in the level of greenhouse gases in the atmosphere
Describe what a climate forcing is and introduce the Earth’s energy balance.
Make sure to explain what I mean by PERTURBATION. E.g prodding some jelly, moving a pen (i’ve perturbed it’s location), a small change.

12. Exercise: Radiative Forcings
This table is adapted from the figure used by the IPCC 5th Assessment Report to describe radiative forcings. Draw on bars to show if the forcing is positive or negative and how large this forcing is.
Introduce the next exercise. Here students need to draw on bars to the figure to indicate the direction and magnitude of the forcing (rough estimates are fine!)
Identify zero line clearly, and demonstrate bar either side
IPCC AR5 Figure SPM.5

13. Radiative Forcings (answer)
Point out Anthropogenic vs natural first. Then talk about uncertainty bars, but also level of confidence of overall direction.
Mention clouds and how this is quite uncertain and still huge area of research.
Here are the forcings as presented in IPCC AR5. The details are not important but the different levels of uncertainty in some areas can be pointed out.
The text from the IPCC SPM is below:
Radiative forcing estimates in 2011 relative to 1750 and aggregated uncertainties for the main drivers of climate change. Values are global average radiative forcing (RF14), partitioned according to the emitted compounds or processes that result in a combination of drivers. The best estimates of the net radiative forcing are shown as black diamonds with corresponding uncertainty intervals; the numerical values are provided on the right of the figure, together with the confidence level in the net forcing (VH – very high, H – high, M – medium, L – low, VL – very low). Albedo forcing due to black carbon on snow and ice is included in the black carbon aerosol bar. Small forcings due to contrails (0.05 W m–2, including contrail induced cirrus), and HFCs, PFCs and SF6 (total 0.03 W m–2) are not shown. Concentration-based RFs for gases can be obtained by summing the like-coloured bars. Volcanic forcing is not included as its episodic nature makes is difficult to compare to other forcing mechanisms. Total anthropogenic radiative forcing is provided for three different years relative to 1750.
IPCC AR5 Figure SPM.5

14. What is a climate feedback?
A climate feedback occurs when an initial process triggers changes in a second process, and that in turn influences the initial one. A positive feedback intensifies the original process and a negative feedback reduces it.
Explain difference between positive and negative feedbacks
Full IPCC AR5 definition:
“An interaction mechanism between processes in the climate system is
called a climate feedback when the result of an initial process triggers
changes in a second process that in turn influences the initial one. A
positive feedback intensifies the original process, and a negative feedback
reduces it.”

15. Climate feedback example
Positive Feedback
Climate change - ice and snow and the albedo effect. Changes in the polar regions can cause more warming in the entire planet earth system through feedback effects. One such effect is the reduction of ice and snow due to warmer temperatures. When the white and gray snow and ice disappears, less sun rays are reflected out and instead the energy is absorbed by land and sea - which causes further increase in the warming.
At this point introduce Exercise 2 – the idea is to get students to think up (and draw) their own examples of both positive and negative climate feedbacks. They can then present these back to the room by sticking them under the appropriate label on a wall and explain their thinking.
Exercise: work in small groups to draw some more examples of feedbacks (positive and negative) in the climate system

16. What are the processes which feedback on the climate?
Processes which represent feedbacks:
This slide can be used to provide ideas for the climate feedback exercise.
Positive
Snow albedo change  warming => less snow / ice => more warming
Arctic Methane release (from permafrost) -> Positive (warming => ice melt => methane release => more warming)
Ocean methane release
Water vapor -> warming => more wv in atmosphere => more warming
Forest fires -> Warmer planet (and drier in some areas) => forest fire more likely => release of carbon => more warming
Ocean carbon absorption -> Increased warming => less carbon absorbed by oceans => more warming.
Negative
Plants: Warming => More plant growth (but does it.. Desertification?) => more carbon absorbed => less warming.
Both / not clear
Clouds: Warming =>more wv in atmosphere => more clouds => more or less warming depending on type of cloud
High cloud => warming (traps more heat, from below than it reflects back from above)
Low cloud => cooling (reflects more heat from above than it traps from below)
Source: Intergovernmental Panel on Climate Change (IPCC), WG1-AR3, Ch 1.

17. 2. Climate variability
So we have seen that the earth has an atmosphere which in turn has an affect but we all know that weather and climate varies – this is the next topic

18. Variations of the Earth’s surface temperature for the past 1000 years
FROM observations...
There has been considerable advance in understanding of the temperature change that occurred over the last millennium
We can see in the figure that the rate and duration of warming of the Northern Hemisphere in the 20th century appears to have been unprecedented during the millennium
Because of less data is available, less is known about the conditions prevailing in the Southern Hemisphere prior to 1861.
SPM 1b

19. Climate variations NATURAL or ANTHROPOGENIC ? Orbital changes
volcanic eruptions (aerosol emission)
greenhouse gases
Aerosol (e.g. sulphates from burning coal)
Ozone pollution
solar radiation
Define NATURAL and ANTHROPOGENIC forcings
Exercise: 3 minutes with partner – decide whether these factors influencing global temperature variation are natural or anthropogenic factors. Decide whether they would have a net cooling or warming effect.
Feed back answers to get those on the slide.
Click on link and scroll through interactive graph.
Explain about each one in some detail:
e.g. Volcanoes - Pinatubo in 1991:
injected significant quantities of aerosols and dust into the stratosphere
the largest since the eruption of Krakatoa in 1883, with a total mass of SO2 of about 17,000,000 t being injected. This very large stratospheric injection resulted in a reduction in the normal amount of sunlight reaching the Earth's surface by roughly 10% (see figure). This led to a decrease in northern hemisphere average temperatures of 0.5–0.6 °C and a global fall of about 0.4 °C, taking 4 years to recover.
Anthropogenic aerosols cause cooling, but also acid rain… not great.
Land-use change (agriculture, deforestation, reforestation, urbanisation, traffic, …)
Which are causing global temperature increases?

20. Carbon dioxide rising CO2 from Ice core records
Carbon dioxide levels are rising fast.
We have observations of past CO2 levels going back 800,000 years from polar ice cores.
As snow compresses to ice pockets of air store a historical record of the atmosphere’s past.
The data from ice cores reveals that carbon dioxide levels vary naturally over timescales of 1000’s and 10,000’s of years.
This reflect that natural exchanges of carbon between the atmosphere, ocean and earth’s surface.
In the early 1700’s the CO2 level in the atmosphere was around 270ppmv; relatively high but well within the bounds of past variations.
Since the industrial revolution CO2 concentrations have risen at unprecedented rates, rising to 400 ppmv in 2013 (about 50% higher than pre-industrial levels).
The concentration is now much higher than it has ever been at any time in the 800,000 year record. 22 22

21. 3. What is a climate model?

22. How can we predict future climate?

23. Example equations for the motion of the atmosphere
These equations stem from the basic laws of motion (Newton) and thermodynamics.
These are intrinsic to all weather and climate models.
Because the atmosphere is very large and turbulent there is no one simple solution for these equations.

24. How do climate models work?
In principle, climate models are a large set of equations describing the physical and chemical processes occurring in the atmosphere, ocean, land, ice... etc
Click on the link to go to a YouTube video from the Met Office channel about climate models.
How do climate models work?

25. Development of climate models
Activity:
Development of climate models
Run the activity here using the print outs of different climate processes. Give a sheet to each student and ask them to line up in order along the room from earliest processes to most recent processes included in a climate model.
Use the next slide to go through the answer.

26. Development of Climate models
Key points:
Our knowledge of the real world has improved, and computer power has increased, allowing us to improve how we represent climate in our models.
In the 1970s, models included a simple representation of the atmosphere. Rain was included but not clouds.
Now, current state-of-the-art climate models include fully interactive clouds, oceans, land surfaces and aerosols. Some models are starting to include detailed chemistry and the carbon cycle.

27. Development of climate models

28. 4. Projected climate change
We’ve established that the climate is changing at an unprecedented rate, and we can use climate models to reproduce observed climate. But we don’t know what the future holds. What we have to do therefore, is consider a range of possible future climates; the IPCC uses RCP scenarios. The choice of RCP scenario which we feed into a climate model will greatly impact the future projections which it produces.

29. Projections of Climate Change
The first thing we need to know is what the emissions will be of greenhouse gases and other gases which affect climate change. These projections are deduced from separate models which take into account population growth, energy use, economics, technological developments, and so forth.
Having obtained projections of how emissions will change, we then calculate how much remains in the atmosphere, i.e. what future concentrations will be. For CO2, this is done using a model of the carbon cycle, which simulates the transfer of carbon between sources (emissions) and sinks in the atmosphere, ocean and land (vegetation). For gases such as methane, we use models which simulate chemical reactions in the atmosphere.
Next we have to calculate the heating effect of the increased concentrations of greenhouse gases; this is often called climate forcing.
This is done within the climate model, which generates spatial patterns of changes in temperature, rainfall and sea level etc., across the surface of the earth and through the depth of the atmosphere and oceans.
Following on from the climate change prediction, the impacts of climate change, on socio-economic sectors such as as water resources, food supply, flooding, can then be calculated.

30. Climate Model Projections
Global warming >2˚C is likely for scenarios with little mitigation of emissions (RCP4.5 and above). No mitigation (RCP8.5) leads to a world more than 4˚C warmer than pre-industrial times
RELATIVE CONCENTRATION PATHWAYS:
RCP8.5: Rising radiative forcing pathway leading to 8.5 W/m2 in (no mitigation)
RCP4.5: Stabilization without overshoot pathway to 4.5 W/m2 at stabilization after 2100 (moderate mitigation)
The number of Coupled Model Intercomparison Project Phase 5 (CMIP5) models used to calculate the multi-model mean is indicated.
IPCC AR5: Global average surface temperature change from 2006 to 2100 as determined by multi-model simulations. All changes are relative to 1986–2005. Time series of projections and a measure of uncertainty (shading) are shown for scenarios RCP2.6 (blue) and RCP8.5 (red).

31. Projected temperature change 2071 to 2100 average, relative to 1990
Strong mitigation scenario No mitigation scenario
Consider which RCP scenario to use in your work; the outputs are likely to be very different. We will sometimes opt for RCP8.5 because it gives the strongest climate change signal, but it is important to consider the range of possible outcomes.
Temperature rises are not at all uniform
Greatest warming in Arctic (where sea-ice melt acts as a positive feedback, show the greatest warming) and over continents.
Southern Ocean warms the least (In these areas there is a rapid exchange of surface water with deep water, which acts as a heat sink to prevent very much surface temperature change.)
Antarctica warms less than the Arctic
8.5 response more significant
Global average 1.9 ºC
Global average 5.5 ºC
Results based on Hadley Centre climate model HadGEM2-ES
(contribution to IPCC 2013)

32. 21C Global average sea level rise
Thermal expansion of water, is the strongest contributor to sea level rise in these projections.
The contribution from melting of polar ice sheets is likely to be within the range 0.03 – 0.20m by 2100.
The Greenland ice sheet stores the equivalent of 6m sea level rise.
Sea levels are projected to go on rising through the 21st Century.
The extent of sea level rise also depends on whether mitigation action is taken to limit global warming.
However, even with strong mitigation of GHG emissions sea levels continue rising through the 21st C.
This is because the ocean takes a long time to come into balance with the new warmer state of the climate.
IPCC AR5: RCP8.5 (no mitigation) and RCP2.6 (strong mitigation) both project continued sea level rise through the 21st Century.

33. Projected regional sea level change : Four RCP scenarios
As we’ve seen with the global temperature and precipitation maps, SLR is not consistent across the world. East coast America
This is why REGIONAL climate models are so important – global averages cannot be assumed to be appropriate for local level impacts.
PRECIS is one such RCM.

34. Questions?
Some extra slides follow which may prove useful in helping to answer questions.

35. How do we quantify the response of the climate?
The response of the climate system to these forcing agents is complicated by:
feedbacks
the non-linearity of many processes
different response times of the different components to a given perturbation
The only means available to calculate the response is by using numerical models of the climate system.
The increase in greenhouse gas and aerosol concentrations in the atmosphere and also land use change produces a radiative forcing or affects processes and feedbacks in the climate system. The response of the climate to these human-induced forcings is complicated by such feedbacks, by the strong non-linearity of many processes and by the fact that the various coupled components of the climate system have very different response times to perturbations. Qualitatively, an increase of atmospheric greenhouse gas concentrations leads to an average increase of the temperature of the surface troposphere system. The response of the stratosphere is entirely different. The stratosphere is characterized by a radiative balance between absorption of solar radiation mainly by ozone, and emission of infrared radiation by mainly carbon dioxide. An increase of the carbon dioxide concentration therefore leads to an increase of the emission and thus to a cooling of the stratosphere.
The only means available to quantify the non-linear climate response is by using numerical models of the climate system based on well- established physical, chemical and biological principles, possibly combined with empirical and statistical methods.

36. The effect of aerosol An examples of uncertainty in predictions
Once in the atmosphere, aerosols have two effects upon climate, both of which lead to a cooling of the Earth:
They can directly reflect sunlight back away from the Earth (left hand panel of Fig 1)
They can interact with clouds in complex ways leading to changes in cloud reflectivity, cloud lifetime, cloud height and cloud precipitation (Fig 1).
The overall impact of aerosols on climate
Human activities have increased concentrations of atmospheric aerosols, which have led to an associated cooling of climate. This cooling acts to counterbalance some of the warming due to increased concentrations of greenhouse gases which are also caused by human activities.
Just how much of a cooling effect these aerosols have on the climate is still uncertain owing to the complexity of the problem (Fig 1); but the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC, 2007) went some way to assessing this. It concluded that, although these microscopic particles do act to cool the climate, they do not offset the global warming effect of greenhouse gases (Fig 2).

37. Earth-system processes in today’s climate models
As previously discussed the climate system is more important than that!
All of these have a part to play and need to be represented in climate models to see how they interact and what the overall consequences are for the behaviour of the climate system and how climate change plays out when the system is perturbed by either a natural or human influence.