[asa] Attributing physical and biological impacts to anthropogenic climate change

The following is in today's Nature. This is not some computer model
projection but current effects of our contemporary modest warming.

Attributing physical and biological impacts to anthropogenic climate
change
http://www.nature.com/nature/journal/v453/n7193/abs/nature06937.html

> Significant changes in physical and biological systems are occurring
> on all continents and in most oceans, with a concentration of
> available data in Europe and North America. Most of these changes
> are in the direction expected with warming temperature. Here we show
> that these changes in natural systems since at least 1970 are
> occurring in regions of observed temperature increases, and that
> these temperature increases at continental scales cannot be
> explained by natural climate variations alone. Given the conclusions
> from the Intergovernmental Panel on Climate Change (IPCC) Fourth
> Assessment Report that most of the observed increase in global
> average temperatures since the mid-twentieth century is very likely
> to be due to the observed increase in anthropogenic greenhouse gas
> concentrations, and furthermore that it is likely that there has
> been significant anthropogenic warming over the past 50 years
> averaged over each continent except Antarctica, we conclude that
> anthropogenic climate change is having a significant impact on
> physical and biological systems globally and in some continents.
>

The authors looked at 77 other studies and did what is known as joint
attribution. Here's an example of one of these studies. More details
can be found here http://www.nature.com/nature/journal/v453/n7193/extref/nature06937-s1.pdf
  [Subscription to Nature required]

> Abu-Asab, M. S., P. M. Peterson, S. G. Shetler and S. S. Orli 2001:
> Earlier plant flowering in spring as a response to global warming in
> the Washington, DC, area. Biodiversity and Conservation 10: 597.
>
> This effect was deemed very unlikely to be due to other driving
> forces than anthropogenic climate change because change related to
> warming and not other factors. Advances in flowering of 89 species
> are directly correlated with local increases in min temperature.
> [RDB Note: very unlikely means 1-10% probability. The vast majority
> of the studies were very unlikely. 10% of the studies were
> exceptionally unlikely that is < 1% probability. 20 studies were
> unlikely 10-30% probability, and 3 studies were likely 66-90%
> probability]

Here's the explanation of their methodology:

> Following the definition of attribution of observed changes in the
> climate system23, changes in physical and biological systems are
> attributed to regional climate change based on documented
> statistical analyses confirmed by process-level understanding in the
> interpretation of results. For example, a statistical association
> between poleward expansion of species' ranges and warming
> temperatures is expected when temperatures exceed physiological
> thresholds. The observed changes in both climate and the natural
> system are demonstrated to be: unlikely to be entirely due to
> natural variability; consistent with the estimated responses of
> either physical or biological systems to a given regional climate
> change; and not consistent with alternative, plausible explanations
> of the observed change that exclude regional climate change.
>
> Attribution of changes in natural systems to anthropogenic warming
> requires further analysis because the observed regional climate
> changes must be attributed to anthropogenic causes. Combining these
> two types of attribution, called 'joint' attribution2, has lower
> statistical confidence than either of the individual attribution
> steps alone.
>
> One approach to joint attribution, which uses what may be called an
> 'end-to-end' method, has already been conducted in several studies
> of specific physical and biological systems. This approach involves
> linking climate models with process-based or statistical models to
> simulate changes in natural systems caused by different climate
> forcing factors, and comparing these directly with observed changes
> in natural systems. When temperature data from the HadCM3 global
> climate model were used to examine the likely cause for changes in
> the timing of spring events of Northern Hemisphere wild animals and
> plants, results show the strongest agreement when the modelled
> temperatures were derived from simulations incorporating
> anthropogenic forcings24. Other similar studies have shown that the
> retreat of two glaciers in Switzerland and Norway cannot be
> explained by natural variability of climate and glacier mass
> balance25, that observed global and Arctic patterns of changes in
> streamflow are consistent with the response to anthropogenic climate
> change26, 27, and that the observed increase in the area of forests
> burned in Canada over the last four decades is consistent with the
> response caused by anthropogenic climate change28.
>
> Here we conduct a joint attribution study across multiple physical
> and biological systems at both the global and the continental scale.
> We demonstrate statistical consistency of observed changes (which
> are very unlikely to be caused by natural internal variability of
> the systems themselves or other driving forces) in natural systems
> with warming and conduct spatial analyses that show that the
> agreement between the patterns of observed significant changes in
> natural systems and temperature changes is very unlikely to be
> caused by the natural variability of the climate (Supplementary Fig.
> 1). Combined with the attribution of global and continental-scale
> warming to anthropogenic climate forcing demonstrated by IPCC
> Working Group I Fourth Assessment Report, this analysis provides
> strong support for joint attribution of observed impacts.
>
>
Rich Blinne
Member ASA

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Received on Thu May 15 09:05:03 2008