In brief: Scientists are hesitant to say that Climate Change will lead for increases in Tornadoes (They have "low confidence" in such a direct cause and effect linkage.)
Partially because the science of Tornado formation is not entirely understood.
Partially because the historical Tornado data is not captured at fine enough data resolution to model accurately to gauge comparative future trends.
And mostly because what they do understand, that the two main factors of Tornado formation (atmospheric moisture and wind shear) seem to be going in opposite, opposing directions as Climate Change kicks in.
Atmospheric moisture is increasing, while Winds are decreasing. The result many scientists say may be a wash -- that the needed ingredients for Tornado formation may end up just cancelling each other out.
Tell that to the folks of Oklahoma eh? May the winds of fate be kind, whenever they DON'T cancel each other out.
Tornadoes and climate change - what does the science say?
by Freya Roberts, carbonbrief.org -- 22 May 2013
How Do Tornadoes Form?
SciAmerican
link to video
[...]
What does the science say?
Trying to establish whether tornadoes activity will change as the climate warms is tricky for a number of reasons, as a recent report from the Intergovernmental Panel on Climate Change (IPCC) highlights.
[...]
Then, there's one final problem. Climate change is likely to affect the two critical conditions for tornado formation -- atmospheric moisture and wind shear -- in opposite ways. The atmosphere is expected to hold more moisture as temperatures rise, making tornadoes more likely. But wind shear will probably decrease, having the opposite effect. Scientists can't say whether one force will override the other.
[...]
It'll be like the battle of MAC Trucks on a 2-lane highway, with no speed limits. Most of the time the opposing trucks will stay in their own lanes. But may the good earth help during us, those times that when they don't -- those times when they just happen to cross over that thin opposing line. That thin white line, enforcing the fragile order of the status quo.
Here's some nitty gritty details from the IPCC report reference in the intro, with a focus on its trend predictions for the extreme weather events, known as tornadoes:
Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (pdf)
Special Report of the Intergovernmental Panel on Climate Change
2012
Extreme weather and climate events, interacting with exposed and vulnerable human and natural systems, can lead to disasters. This Special Report explores the challenge of understanding and managing the risks of climate extremes to advance climate change adaptation. Weather- and climate-related disasters have social as well as physical dimensions. As a result, changes in the frequency and severity of the physical events affect disaster risk, but so do the spatially diverse and temporally dynamic patterns of exposure and vulnerability. Some types of extreme weather and climate events have increased in frequency or magnitude, but populations and assets at risk have also increased, with consequences for disaster risk. Opportunities for managing risks of weather- and climate-related disasters exist or can be developed at any scale, local to international. Some strategies for effectively managing risks and adapting to climate change involve adjustments to current activities. Others require transformation or fundamental change.
[pg 6]
larger image
[pg 13]
There is medium confidence that there will be a reduction in the number of extratropical cyclones averaged over each hemisphere. While there is low confidence in the detailed geographical projections of extratropical cyclone activity, there is medium confidence in a projected poleward shift of extratropical storm tracks. There is low confidence in projections of small spatial-scale phenomena such as tornadoes and hail because competing physical processes may affect future trends and because current climate models do not simulate such phenomena. [3.3.2, 3.3.3, 3.4.5]
[pg 40]
Weather and climate phenomena reflect the interaction of dynamic and thermodynamic processes over a very wide range of space and temporal scales. This complexity results in highly variable atmospheric conditions, including temperatures, motions, and precipitation, a component of which is referred to as ‘extreme events.’ Extreme events include the passage of an intense tornado lasting minutes and the persistence of drought conditions over decades -- a span of at least seven orders of magnitude of timescales. An imprecise distinction between extreme ‘weather’ and ‘climate’ events, based on their characteristic timescales, is drawn in Section 3.1.2. Similarly, the spatial scale of extreme climate or weather varies from local to continental.
[pg 41]
1.2.3. Extreme Impacts
1.2.3.1. Three Classes of Impacts
In this subsection we consider three classes of ‘impacts’:
1) changes in the natural physical environment, like beach erosion from storms and mudslides;
2) changes in ecosystems, such as the blow-down of forests in hurricanes, and
3) adverse effects (according to a variety of metrics) on human or societal conditions and assets.
However, impacts are not always negative: flood-inducing rains can have beneficial effects on the following season’s crops (Khan, 2011), while an intense freeze may reduce insect pests at the subsequent year’s harvest (Butts et al., 1997).
An extreme impact reflects highly significant and typically long-lasting consequences to society, the natural physical environment, or ecosystems. [...] Whether an extreme event results in extreme impacts on humans and social systems depends on the degree of exposure and vulnerability to that extreme, in addition to the magnitude of the physical event (high confidence).
[...]
[pg 42]
Disaster signifies extreme impacts suffered by society, which may also be associated with extreme impacts on the physical environment and on ecosystems. Building on the definition set out in Section 1.1.2.1, extreme impacts resulting from weather, climate, or hydrological events can become disasters once they surpass thresholds in at least one of three dimensions: spatial -- so that damages cannot be easily restored from neighboring capacity; temporal -- so that recovery becomes frustrated by further damages; and intensity of impact on the affected population -- thereby undermining, although not necessarily eliminating, the capacity of the society or community to repair itself (Alexander, 1993). However, for the purposes of tabulating occurrences, some agencies only list ‘disasters’ when they exceed certain numbers of killed or injured or total repair costs (Below et al., 2009; CRED, 2010).
[pg 150]
Over North America, a declining trend in 50th and 90th percentile wind speeds has been reported for much of the United States over 1973 to 2005 (Pryor et al., 2007) and in 10-m hourly wind data over 1953-2006 over western and most of southern Canada (Wan et al., 2010). An increasing trend has been reported in average winds over Alaska over 1955-2001 by Lynch et al. (2004) and over the central Canadian Arctic in all seasons and in the Maritimes in spring and autumn by Wan et al. (2010) as well as in annual maximum winds in a regional reanalysis over the southern Maritimes from 1979-2003 (Hundecha et al., 2008). Over China, negative trends have been reported in 10-m monthly mean and 95th percentile winds over 1969-2005 (Guo et al., 2011), [...]
Trends in extreme winds have also been inferred from trends in particular phenomena. With regards to tropical cyclones (Section 3.4.4.), no statistically significant trends have been detected in the overall global annual number although a trend has been reported in the intensity of the strongest storms since 1980 [but there is low confidence that any observed long-term (i.e., 40 years or more) increases in tropical cyclone activity are robust, after accounting for past changes in observing capabilities; see Section 3.4.4]. In the mid-latitudes, studies have used proxies for wind such as pressure tendencies or geostrophic winds calculated from triangles of pressure (geo-winds) [...] Regarding other phenomena associated with extreme winds, such as thunderstorms, tornadoes, and mesoscale convective complexes, studies are too few in number to assess the effect of their changes on extreme winds. As well, historical data inhomogeneities mean that there is low confidence in any observed trends in these small-scale phenomena.
It is really a sad commentary on our once scientifically-driven society, that we have been reduced to finding and adopting the most appropriate Adaptation and Risk Management strategies --
as our way of "dealing with Climate Change."
Images of a panicky Fire-drill reactive planning models come to mind.
Link
And sadder yet is, we probably will put off Adaptation and Mitigation implementation too, until its ultimate toll on Society is far, far too much for any of us to adequately bear -- in one lump sum. Of paying the Climate Piper.
On a personal note, it is hard for me to imagine a world with diminishing winds. It just doesn't seem right, that this apathetic path, which as a society we have casually chosen on the unfounded claims of Climate Denial, instead of warnings of actual Climate Science. As if this grand experiment in Global Climate forcing, had a Reset Button, which when we finally wake up, and don't like its society-impacting results -- we could just somehow magically push.
And inanely say "Do over, Please."
Sadly the Climate System is more like a super-tanker heading for an Ice Field, than it is a speed boat, that can weave among the buoys on a whim.
Link
Lead time is the critical factor, in systems with such mass and inertia. A factor that somehow, we have conveniently managed to ignore. To our extreme weather peril.