RELIABILITY OF CLIMATE MODELS
Climate models are even more accurate than you thought | Dana Nuccitelli
Corresponding paper
Robust comparison of climate models with observations using blended land air and ocean sea surface temperatures
Till now there has been a discrepancy between what was being measured as data and model that caused some mismatch between model and data.
In previous evaluations like the one done by the IPCC, climate model simulations of global surface air temperature were compared to global surface temperature observational records like
HadCRUT4.
However, over the oceans, HadCRUT4 uses sea surface temperatures rather than air temperatures.
Thus looking at modeled air temperatures and HadCRUT4 observations isn’t quite an apples-to-apples comparison for the oceans
. As it turns out, sea surface temperatures haven’t been warming fast as marine air temperatures, so this comparison introduces a bias that makes the observations look cooler than the model simulations.
This difference has now been corrected.
The new study addresses this problem by
instead blending the modeled air temperatures over land with the modeled sea surface temperatures to allow for an apples-to-apples comparison.
But this is not all. The increasingly open ocean on the Arctic also changes which temperature is being measured there.
The authors also identified another challenging issue for these model-data comparisons in the Arctic. Over sea ice, surface air temperature measurements are used, but for open ocean, sea surface temperatures are used. As co-author Michael Mann notes,
as Arctic sea ice continues to melt away, this is another factor that accurate model-data comparisons must account for.
The models had projected a 0.226°C per decade global surface air warming trend for 1975–2014 (and 0.212°C per decade over the geographic area covered by the HadCRUT4 record).
However, when matching the HadCRUT4 methods for measuring sea surface temperatures, the modeled trend is reduced to 0.196°C per decade. The observed HadCRUT4 trend is 0.170°C per decade.So when doing an apples-to-apples comparison, the difference between modeled global temperature simulations and observations is 38% smaller than previous estimates.
The result far better match of data and models now that both have the same inputs
Note that this is without considering the new 2015 and 2016 data that moves the black line above the model mean. Here is how it looks
CMIP5 is the most reliable model based upon an international collaboration of 20 climate modeling labs going on since 2008. It is based at Lawrence Livermore National laboratory. The fidelity of the model is all to obvious. Here is more about CMIP5
CMIP5 - Overview
CMIP5 - Coupled Model Intercomparison Project Phase 5 - Overview
At a September 2008 meeting involving 20 climate modeling groups from around the world, the WCRP's Working Group on Coupled Modelling (
WGCM), with input from the
IGBP AIMES project, agreed to promote a new set of coordinated climate model experiments. These experiments comprise the fifth phase of the Coupled Model Intercomparison Project (CMIP5). CMIP5 will notably provide a multi-model context for 1) assessing the mechanisms responsible for model differences in poorly understood feedbacks associated with the carbon cycle and with clouds, 2) examining climate “predictability” and exploring the ability of models to predict climate on decadal time scales, and, more generally, 3) determining why similarly forced models produce a range of responses.
It is expected that some of the scientific questions that arose during preparation of the Intergovernmental Panel on Climate Change (
IPCC) Fourth Assessment Report (AR4) will through CMIP5 be addressed in time for evaluation in the Fifth Assessment Report (AR5, scheduled for publication in late 2013). The
IPCC/CMIP5 schedule (
pdf ) is now available and the three key dates are as follows:
- Februrary 2011: First model output is expected to be available for analysis,
- July 31, 2012: By this date papers must be submitted for publication to be eligible for assesment by WG1,
- March 15, 2013: By this date papers cited by WG1 must be published or accepted.
The IPCC’s AR5 is scheduled to be published in
September 2013. Future timeline information can be found on
IPCC WG1 website.
CMIP5 is meant to provide a framework for coordinated climate change experiments for the next five years and thus includes simulations for assessment in the AR5 as well as others that extend beyond the AR5. CMIP5 is not, however, meant to be comprehensive; it cannot possibly include all the different model intercomparison activities that might be of value, and it is expected that various groups and interested parties will develop additional experiments that might build on and augment the experiments described here.
CMIP5 promotes a standard set of model simulations in order to:
- evaluate how realistic the models are in simulating the recent past,
- provide projections of future climate change on two time scales, near term (out to about 2035) and long term (out to 2100 and beyond), and
- understand some of the factors responsible for differences in model projections, including quantifying some key feedbacks such as those involving clouds and the carbon cycle
