Sunday, January 26, 2014

ExClimate: Climate modelling Australian climate impact scenarios

This article is a little bit of a tangent to my regular articles. I am presently doing an online course - Climate Change: Challenges and solutions - offered by the University of Exeter (UK). So please indulge me as I also use this blog for some climate course work. This article is for week 3, section 3.4 of the course on 'Your Warming World'.

The USGS provides an application, the CMIP5 Global Climate Change Viewer, for anyone to access to do research, with the proviso any results that are published should remain open and non-commercial. This application provides projections for two variables: temperature and precipitation. It can be run for annual mean or monthly results, using the mean model or a selected specific global climate model, and for different projected emissions pathways (Representative Concentration Pathways or RCP) for a particular period.

It might sound complicated, but the tool is relatively easy to use, but takes a little while to figure out all the bells and whistles. I did an initial investigation and produced some basic results, but after sleeping and some reflection decided to investigate further not only global climate model projections for the planet, but also regional projections for the South East Asia and the South Pacific and Australia in particular.

Representative Concentration Pathways (RCP)

Representative Concentration Pathways (RCP) are models and projections for different emissions pathways. We have a choice in managing climate change and setting the earth's thermostat. If we do nothing, we choose by default business as usual with rising emissions - that too is a considered choice and pathway that approximates to RCP 8.5. This leads to an end of century average global temperature anomaly of 4.9C. Actually, current emission rates would have us tracking above the RCP8.5 pathway.

If we take a global crash course in rapid and substantial emissions reduction immediately in 2014, the pathway would look something like RCP 2.6. This would be the equivalent of changing production at the start of World War 2, involving major economic transition and economic regulation to reduce emissions. It is quite feasible but comes with social costs of sacificing some economic comfort now for long term comfort of society. A one degree war as advocated by Jorgen Randers and Paul Gilding. This would allow us to meet the agreed target of keeping climate change below 2 degrees of warming, the one positive commitment that did come out of Copenhagen in 2009. The window of opportunity may already be closing on this pathway.

There are two intermediate pathways, RCP 4.5 and RCP 6.0 that varying degrees of mitigation that lead to an end of century temperature anomaly of 2.4 or 3 degrees C - in the danger zone. Why is it in the danger zone? Because the more warming we cause, the greater the liklihood we will trigger major climate system tipping points such as large scale Arctic methane release, abrupt collapse of ice sheets, destabilisation of the East Asian or Indian monsoons, intensification of El Nino cycle.

The Skeptical Science website has a Beginner's Guide to Representative Concentration Pathways by GP Wayne for an in depth look at exploring the differences in the pathways. A quick comparison comparing the different pathways comes from Part 3: technical summary:.

Each Representative Concentration Pathway (RCP) defines a specific emissions trajectory and subsequent radiative forcing (a radiative forcing is a measure of the influence a factor has in altering the balance of incoming and outgoing energy in the Earth-atmosphere system, measured in watts per square metre):

Table 4: from Moss et.al. 2010. Median temperature anomaly over pre-industrial levels and SRES comparisons based on nearest temperature anomaly, from Rogelj et.al. 2012 Source: Skeptical Science

Professor of Computer Science at Cornel University Stuart Staniford argues in a January 2013 blog post on The Human Response Function to Climate Change that we don't yet have the widespread social concern to pursue RCP 2.6. He is also critical of the intermediate pathways. He thinks once the impacts of extreme weather really bite over the next 10-15 years, people will clamour for solutions and the political will to tackle the problem will come together. He thinks a pathway rising to a peak about 2030, will then fall rapidly to zero emissions by 2080 as people clamour for substantive action. It takes account of human behaviour and psychology, while Staniford also recognises that this is an extremely risky path.

Back to my modelling experiments.


First model results: RCP8.5 for 2050-2074

My initial play with Global climate models I came up with these results:

CMIP5 mean model Annual mean using RCP8.5 for 2050-2074 for all results Temperature For Australia shows a mean increase of 2.7C Precipitation For Australia shows no change in precipitation. I noted that Changes in precipitation are likely to occurr on a regional level and balance out on a national basis.

Canada and Russia As expected, high Arctic countries have the highest annual temperature increases: Canada shows 4.5C, Russia shows 4.6C Precipitation: Both Russia and Canada experience a 0.2mm/day increase in precipitation.

The model results also show tropical countries with higher precipitation: Malaysia on 0.5mm/day, Indonesia, Papua, Ecuador on 0.4mm/day

Some subtropical countries experience a rainfal deficit: Brazil, Bolivia Zambia, Morocco, France on -0.1mm/day, Mexico, Spain, Chile -0.2mm/day, Venezuela -0.3mm/day

This appears to confirm the global trend that the sub tropical arid regions will get dryer while the tropics and sub-polar latitudes will get wetter.

Very basic first results using the model mean and for an intermediate period this century. That was my practice run. I wanted to be a little more systematic so produced results again for RCP8.5 for 2071-2095


Business As Usual results for 2071-2095

CMIP5 mean model Annual mean using RCP8.5 for 2071-2095 for all results

Australasia

  • Australia: Temp 3.8C Precipitation: 0mm/day
  • Christmas Is: Temp 2.7C Precipitation: -0.1mm/day
  • Cocos Is: Temp 2.7C Precipitation: 0mm/day
  • Norfolk Is: Temp 2.7C Precipitation: -0.2mm/day
  • Heard and McDonald Is: Temp 2.2C Precipitation: 0.5mm/day

Major CO2 Emitters

  • Canada: Temp 6.3C Precipitation: 0.3mm/day
  • Russia: Temp 6.3C Precipitation: 0.3mm/day
  • China: Temp 4.8C Precipitation: 0.3mm/day
  • USA: Temp 5C Precipitation: 0.2mm/day
  • India: Temp 3.9C Precipitation: 0.4mm/day

South East Asia

  • Malaysia: Temp 3.1C Precipitation: 0.7mm/day
  • Indonesia: Temp 3.1C Precipitation: 0.6mm/day
  • Papua: Temp 2.7C Precipitation: 0.5mm/day
  • Philippines: Temp 2.9 C Precipitation: 0.6mm/day

South Western Pacific

  • Fiji: Temp 2.6 C Precipitation: 0.4mm/day
  • French Polynesia: Temp 2.6 C Precipitation: 0.5mm/day
  • Kiribati: Temp 3.0 C Precipitation: 1.1mm/day
  • Marshall Is: Temp 2.7 C Precipitation: 0.6mm/day
  • Micronesia: Temp 2.7 C Precipitation: 0.7mm/day
  • Nauru: Temp 2.9 C Precipitation: 1.3mm/day
  • New Caledonia: Temp 2.6 C Precipitation: 0.2mm/day
  • New Zealand: Temp 2.9C Precipitation: 0.1mm/day
  • Pitcairn Is: Temp 1.9 C Precipitation: -0.7mm/day
  • Samoa: Temp 2.6 C Precipitation: 0.2mm/day
  • Tokelau: Temp 2.6 C Precipitation: -0.2mm/day
  • Tonga: Temp 2.5 C Precipitation: 0.3mm/day
  • Tuvalu: Temp 2.6 C Precipitation: -0.1mm/day
  • Vanuatu: Temp 2.6 C Precipitation: 0.3mm/day

As expected, high Arctic countries have the highest annual temperature increases combined with increase in precipitation.

This appears to confirm the global trend that the sub tropical arid regions will get dryer while the tropics and sub-polar latitudes will get wetter.

Precipitation For Australia shows no change. Changes in precipitation are likely to occur on a regional level and perhaps balance out on a national basis. But Some individual models show Australia becoming drier (up to -0.4mm/day drier) and some wetter (FGOALS_G2 and NorESM1-M both predict 0.5mm/day rainfall increase).

If in a warming world the sub-tropical latitudes which already contain deserts are to get even drier, I wanted a Global Climate model that would show this, particularly in regard to Australia. Global climate Model mean results are sometimes not the best predictor for regional climates.

Now, I wanted to refine my results by perhaps using an atmosphere ocean model better representing Australia and the Pacific region. This CSIRO wiki page reviews Global climate models and ideally I wanted to use a model that is refined and focussed on the Australian Pacific region.

I narrowed my selection down to the following 4 Global climate models: GFDL-ESM2M, GISS-E2-H, MPI-ESM-MR, HadGem2-AO. Of these four I chose to use the GFDL-ESM2M.

Part of the reason I chose this global climate model was it's emphasis on deep ocean layer dynamics drawing upon the influence of El Nino Southern Oscillation. (John P. Dunne et al 2012) describe both the GFDL-ESM2M and GFDL-ESM2G global models in their paper - GFDL’s ESM2 Global Coupled Climate–Carbon Earth System Models. Part I: Physical Formulation and Baseline Simulation Characteristics. Here is an excerpt from the abstract:

Differences in the ocean mean state include the thermocline depth being relatively deep in ESM2M and relatively shallow in ESM2G compared to observations. The crucial role of ocean dynamics on climate variability is highlighted in El Niño–Southern Oscillation being overly strong in ESM2M and overly weak in ESM2G relative to observations. Thus, while ESM2G might better represent climate changes relating to total heat content variability given its lack of long-term drift, gyre circulation, and ventilation in the North Pacific, tropical Atlantic, and Indian Oceans, and depth structure in the overturning and abyssal flows, ESM2M might better represent climate changes relating to surface circulation given its superior surface temperature, salinity, and height patterns, tropical Pacific circulation and variability, and Southern Ocean dynamics. The overall assessment is that neither model is fundamentally superior to the other, and that both models achieve sufficient fidelity to allow meaningful climate and earth system modeling applications. This affords the ability to assess the role of ocean configuration on earth system interactions in the context of two state-of-the-art coupled carbon–climate models.

Recent research shows that El Niño Southern Oscillation (ENSO) is likely to intensify and become more frequent with global warming. Research published in January 2014 indicates that Global warming is doubling the risk of Extreme El Ninos. This would seem to validate using the GFDL- ESM2M global climate model.

Here are my results for running GFDL-ESM2M using RCP8.5 for 2071-2095 for all results


GFDL-ESM2M Single model results using RCP8.5 for 2071-2095

GFDL-ESM2M model Annual mean using RCP8.5 for 2071-2095 for all results

Australasia

  • Australia: Temp 3.7C Precipitation: -0.4mm/day
  • Christmas Is: Temp 2.3C Precipitation: -0.5mm/day
  • Cocos Is: Temp 2.1C Precipitation: -0.2mm/day
  • Norfolk Is: Temp 2.1C Precipitation: -0.2mm/day
  • Heard and McDonald Is: Temp 1.3C Precipitation: 0.5mm/day

Major CO2 Emitters

  • Canada: Temp 3.9C Precipitation: 0.2mm/day
  • Russia: Temp 4.5C Precipitation: 0.2mm/day
  • China: Temp 3.5C Precipitation: 0.2mm/day
  • USA: Temp 3.5C Precipitation: 0.1mm/day
  • India: Temp 3.6C Precipitation: 0mm/day

South East Asia

  • Malaysia: Temp 2.4C Precipitation: 0.7mm/day
  • Indonesia: Temp 2.5C Precipitation: 0.6mm/day
  • Papua: Temp 2.2C Precipitation: 1.0mm/day
  • Philippines: Temp 2.5 C Precipitation: 1.7mm/day

South Western Pacific

  • Fiji: Temp 2.4 C Precipitation: 1.3mm/day
  • French Polynesia: Temp 2.2 C Precipitation: 0.6mm/day
  • Kiribati: Temp 3.0 C Precipitation: -0.8mm/day
  • Marshall Is: Temp 2.9 C Precipitation: 0.6mm/day
  • Micronesia: Temp 2.8 C Precipitation: 1.0mm/day
  • Nauru: Temp 3.2 C Precipitation: -0.8mm/day
  • New Caledonia: Temp 2.3 C Precipitation: 0.1mm/day
  • New Zealand: Temp 2.1C Precipitation: 0mm/day
  • Pitcairn Is: Temp 1.6 C Precipitation: -0.9mm/day
  • Samoa: Temp 2.6 C Precipitation: 0.4mm/day
  • Tokelau: Temp 2.6 C Precipitation: -0.2mm/day
  • Tonga: Temp 2.2 C Precipitation: 1.0mm/day
  • Tuvalu: Temp 2.6 C Precipitation: -0.9mm/day
  • Vanuatu: Temp 2.5 C Precipitation: 0.7mm/day

Precipitation for 2049:

Precipitation for 2095:

Temperatures for 2049:

Temperatures for 2095

The GFDL ESM2M Single model results for 2049 and 2095 identify a growing tropical region north of Australia in the coral sea becoming substantially wetter. This may impact on the northern Australian climate.

The GFDL ESM2M global climate model also projects colder ocean waters in the North Atlantic off the south east Greenland. Substantial ocean cooling also occurs in the Weddell Sea, Bellingshausen Sea, and Amundsen Sea off the coast of Antarctica - near the West Antarctic ice sheet which is showing signs of accelerating ice mass loss. These cool spots may reflect increasing dissolution of ice mass from the ice sheets resulting in cooling ocean waters.

Trends in ice sheet loss. Source: Hansen (2012)


Introduction to Australian climate projections

In my research of an appropriate global climate model to use for regional climate scenario for Australia I came across the CSIRO OzClim website. The Commonweath Scientific Industrial Research Organisation (CSIRO), along with the Bureau of Meteorology does much of the directly funded climate research in Australia. This particular online application uses Global Climate models for temperature and rainfall projects for regional Australian modelling. Registration is required, but the tool is free to use once registered. Read more about the OzClim Climate Change Scenario Generator.

The CSIRO application has a step by step scenario generator which uses particular models for different impacts and emission pathways:

For general assessments considering Australia as a whole, we recommend the following combinations of Global Climate Model, rate of global warming and emission scenario to represent a low, moderate and high impact scenario.

Low impact = MUIB/KMA: ECHO-G Global Climate Model with low rate of global warming and B1 emission scenario

Moderate impact = Max Planck: ECHAM5/MPI-OM Global Climate Model with moderate rate of global warming and A1B emission scenario

High impact = GFDL: GFDL-CM2.1 Global Climate Model with high rate of global warming and A1FI emission scenario.


Projections for Australia using GFDL CM2.1 global climate model

I chose scenarios involving business as usual RCP 8.5 (SRES Marker Scenario A1F1) for 2095 to maximise the worst case scenario. Australia is presently doing very little mitigation action, and with the election of Tony Abbott as Prime Minister mitigation action and commitments are being scaled down. So for all intents we are proceeding on the business as usual RCP pathway or worse and these scenarios are the likely result. Also the latest research on clouds indicates that climate sensitivity may be towards the high end of the IPCC range, so I chose a high rate of global warming for the scenarios.

Here is what the temperature increase looks like for 2095 using the GFDL CM2.1 global climate model:

I used the same model and settings to produce a rainfall projection. As most of Australia sits in the 20-40 degrees south zone it is likely to get more drier overall with global warming. The results are rather dramatic for rainfall scenario for 2095 using the GFDL CM2.1 global climate model showing substantial rainfall deficits across much of Australia:


Projections for Australia using ECHAM5/MPI-OM global climate model

CSIRO point out in the FAQ for the OzClim application that "Care must be exercised to preserve the internal consistency of a model’s projections of different climate variables. Variables such as temperature, rainfall, evaporation, and humidity are highly interactive, meaning a change in one variable has an effect on other variables. As such, mixing variables from different models in a single scenario may result in physically implausible (or impossible) combinations."

So I decided to run a different climate model, but one also with strong atmosphere and ocean components. I produced temperature and rainfall projections for Australia for 2095 also with the Max Planck Institute ECHAM5/MPI-OM global climate model.

The rainfall projection for 2095 using the ECHAM5/MPI-OM global climate model:

The temperature projection for 2095 using the ECHAM5/MPI-OM global climate model:


Conclusions

In both scenarios using the GFDL CM2.1 and ECHAM5/MPI-OM global climate models, the south west of Western Australia and eastern and south eastern Australia will have substantial rainfall deficits. While projected temperature patterns are similar in both scenarios, the projected rainfall pattern has substantial differences.

While there is substantial drying in both model projections, the drying on Australia's east coast and northern Australia is particularly accentuated in the GFDL global climate model. The Max Planck global Climate model shows less drying overall, but identifies possible increases of rainfall across parts of the top end.

For Australia, there is already an observational trend over the last 40 years for the south west, south east, and eastern coastal regions of the continent to become drier. Parts of northern Australia may be wetter than they are now with monsoon rains and the ECHAM5/MPI-OM model reflects this. See the Australian Bureau of Meteorology rainfall trend map for 1970-present below:

These scenarios don't paint a very nice picture either for the global climate or Australian climate.

For Australia high temperatures will impact agricultural production and increase the fire weather for bushfires. Reduced rainfall will also reduce water availability for agricultural productivity and drinking. It will make ground water far more valuable for rural towns and for agriculture.

Add in to the mix the recent major development of Coal Seam Gas using fracking technologies contaminating ground water in western New South Wales and Queensland, and new coal mines on the NSW Liverpool plains and in Queensland's Galilee basin which will lower the water table by several meters and alter groundwater flow. These developments will reduce groundwater availability for agriculture possibly setting Australia up for a major food production and water crisis this century.