Global Warming - Science's Double-Standard ?

[Michael Hardner]

Why is it ok, during a heatwave to say:

""It's part of an overall trend," says Jay Lawrimore, climate analysis chief at NOAA's National Climatic Data Center. "Global temperatures ... have been rising for the last 100-plus years. Much of the increase is due to increases in greenhouse gases.""

in the USA Today but when skeptics bring up cold winter weather, they are told "that is weather, not climate"?

Isn't this a double standard ?

[GostHacked]

Looks that way to me.

Climate is specific in many cases to a geographical area. Weather is just a general term we use to encompass all conditions, well to me anyways.

[Shady]

Why is it ok, during a heatwave to say:

in the USA Today but when skeptics bring up cold winter weather, they are told "that is weather, not climate"?

Isn't this a double standard ?

Good post! Yep, it definitely seems like a double standard. When skeptics cite a cold winter, usually they're told that weather is different than climate. But when weather, such as a hot summer takes place. It's proof of global warming. It seems they like to have it both ways. Now, if this summer had been unusally cool, like the summer of 2004, it would be downplayed as again, just weather, and not the same as climate.

It's like one of those carnival shell games.

[Michael Hardner]

Good post! Yep, it definitely seems like a double standard. When skeptics cite a cold winter, usually they're told that weather is different than climate. But when weather, such as a hot summer takes place. It's proof of global warming. It seems they like to have it both ways. Now, if this summer had been unusally cool, like the summer of 2004, it would be downplayed as again, just weather, and not the same as climate.

It's like one of those carnival shell games.

I've been waiting to post this since winter.

Of course, as you know I believe in AGW however I think that it's pointless to promote good science if we don't promote good dialogue surrounding it.

[eyeball]

Perhaps they should have called it atmospheric energizing or something to capture the fact that more carbon essentially traps more of the sun's energy. The fact that energy is also heat is secondary really. It stands to reason that an atmosphere with more energy in it will result in both hotter heat waves and colder cold snaps along the trend line towards an even more energetic atmosphere in the future, given the way things are going.

I ascribe much of the confusion about what's happening to the way our language can play tricks on our perceptions. I mean, people see what they want to see all the time right?

[Michael Hardner]

I ascribe much of the confusion about what's happening to the way our language can play tricks on our perceptions. I mean, people see what they want to see all the time right?

Also to the fact that certain types of people don't get along, and will seize upon a real issue, in order to express revulsion for their enemies.

[TimG]

Of course, as you know I believe in AGW however I think that it's pointless to promote good science if we don't promote good dialog surrounding it.

You want to promote good science yet you make a declaration like 'you believe in AGW'?

Plenty, if not most, skeptics agree that humans affect climate. The debate is how much and whether there is anything we can/should do about it. The fact that people see the need to summarize complex scientific topics with meaningless statements of belief is a bigger problem than confusing weather and climate.

Edited July 17, 2010 by TimG

[TimG]

It stands to reason that an atmosphere with more energy in it will result in both hotter heat waves and colder cold snaps along the trend line towards an even more energetic atmosphere in the future, given the way things are going.

In the past weather was blamed on witches and demons. Today we have CO2. Nothing has changed except the superstitious have learned how to use pseudo scientific lingo to give their superstitions a veneer of respectability.

To illustrate why I think your claim is dubious I suggest you look at the radiative forcing of CO2:

http://en.wikipedia.org/wiki/Greenhouse_gas

It has increase by 1.46 W/m2 since 1750.

The daily energy from the sun is 1366 W/m2

Solar radiation varies between about 1365.5 and 1366.5 over the solar cycle.

http://en.wikipedia.org/wiki/Solar_variation

This means the CO2 effect on the 'energy in the atmosphere' is the same order of magnitude as natural changes in solar output. It therefore follows that we should see increase heat waves/cool spells during every solar maximum.

We don't which suggests your argument is something which was made up to suit a political argument .

Edited July 17, 2010 by TimG

[waldo]

Why is it ok, during a heatwave to say:

It's part of an overall trend," says Jay Lawrimore, climate analysis chief at NOAA's National Climatic Data Center. "Global temperatures ... have been rising for the last 100-plus years. Much of the increase is due to increases in greenhouse gases

in the USA Today but when skeptics bring up cold winter weather, they are told "that is weather, not climate"?

Isn't this a double standard?

Michael, of course, your posting history shows an acceptance that (relatively) recent warming, as represented by demonstrated temperature trends, is significantly caused by GHG’s, in particular anthropogenic based CO2.

Based on your offered quote, I suggest your OP has the wrong emphasis. Certainly, a NOAA rep wouldn’t improperly conflate climate with weather… to me, that quote speaks more to the issue of extreme events and an overall trend of increased frequency and/or intensity as attributed to AGW climate change. As the NOAA rep states, “It’s part of an overall trend”…

[waldo]

Of course, as you know I believe in AGW...

You want to promote good science yet you make a declaration like 'you believe in AGW'?

Plenty, if not most, skeptics agree that humans affect climate. The debate is how much and whether there is anything we can/should do about it. The fact that people see the need to summarize complex scientific topics with meaningless statements of belief is a bigger problem than confusing weather and climate.

Michael, the fact that (some) people see the need to word police is an unnecessary meaningless distraction… certainly, your stating an open acceptance in the validity of AGW causes an adverse reaction from (some) self avowed “sceptics”.

[waldo]

Perhaps they should have called it atmospheric energizing or something to capture the fact that more carbon essentially traps more of the sun's energy. The fact that energy is also heat is secondary really. It stands to reason that an atmosphere with more energy in it will result in both hotter heat waves and colder cold snaps along the trend line towards an even more energetic atmosphere in the future, given the way things are going.

I ascribe much of the confusion about what's happening to the way our language can play tricks on our perceptions. I mean, people see what they want to see all the time right?

In the past weather was blamed on witches and demons. Today we have CO2. Nothing has changed except the superstitious have learned how to use pseudo scientific lingo to give their superstitions a veneer of respectability.

To illustrate why I think your claim is dubious I suggest you look at the radiative forcing of CO2: It has increase by 1.46 W/m2 since 1750.

The daily energy from the sun is 1366 W/m2. Solar radiation varies between about 1365.5 and 1366.5 over the solar cycle.

This means the CO2 effect on the 'energy in the atmosphere' is the same order of magnitude as natural changes in solar output. It therefore follows that we should see increase heat waves/cool spells during every solar maximum.

We don't which suggests your argument is something which was made up to suit a political argument.

oh my! Pseudo scientific would be a step up from your latest reach to attach a superstition motive to those that accept CO2 as the principal causal link for AGW climate change. Equating witches and demons to CO2 – really? I can appreciate you can’t argue on the science, but…….

you totally confused an equilibrium versus change scenario in our recent CO2 sensitivity discussions… as you now do in attaching a balanced carbon cycle condition to your presumptive comparison of the effects of CO2 versus the sun. Apparently, you have never heard of the carbon cycle imbalance caused by human CO2 emissions… of the enhanced greenhouse effect from CO2. Bloody amazing - go figure!

would you care to substantiate your inferred claim that the sun is the causal link to the (relatively) recent warming?

you keep offering cursory, veiled innuendo-like references attempting to link science/scientists to political arguments, to politicization. C’mon man, spit it out… get it over with… get it off your chest. Cathartic and all that!

[TimG]

oh my! Pseudo scientific would be a step up from your latest reach to attach a superstition motive to those that accept CO2 as the principal causal link for AGW climate change. Equating witches and demons to CO2 – really?

As usual you don't bother to read what was written and insert some irrelevant strawman.

If you look at the post that I responded to you will find an assertion that:

"It stands to reason that an atmosphere with more energy in it will result in both hotter heat waves and colder cold snaps".

This assertion has nothing to with the presumed causal link between CO2 and warming. It is pure speculation about the likely effects of that warming. It particular, he made the assertion that 'more energy' = 'colder cold snaps'.

One quick way to examine the plausibility of such speculation is to do a back of the envelope calculation. In this case, the argument was CO2 causes energy to increase which causes more cold snaps. I pointed out that every 11 years the amount of energy being received by the earth increases by about the same amount. If the assertion had any merit one would expect 'colder cold snaps' whenever the solar cycle was at its peak. I am not aware of any such connection in the historical record.

Now none of this this argues against the theory that more CO2 means warmer temperatures on average. What is does argue against long established human tradition of attributing causes to what are random events. In less enlightened times the supernatural would be the cause - today it is pseudo science.

[waldo]

oh my! Pseudo scientific would be a step up from your latest reach to attach a superstition motive to those that accept CO2 as the principal causal link for AGW climate change. Equating witches and demons to CO2 – really? I can appreciate you can’t argue on the science, but…….

As usual you don't bother to read what was written and insert some irrelevant strawman.

If you look at the post that I responded to you will find an assertion that:

"It stands to reason that an atmosphere with more energy in it will result in both hotter heat waves and colder cold snaps".

This assertion has nothing to with the presumed causal link between CO2 and warming. It is pure speculation about the likely effects of that warming. It particular, he made the assertion that 'more energy' = 'colder cold snaps'.

One quick way to examine the plausibility of such speculation is to do a back of the envelope calculation. In this case, the argument was CO2 causes energy to increase which causes more cold snaps. I pointed out that every 11 years the amount of energy being received by the earth increases by about the same amount. If the assertion had any merit one would expect 'colder cold snaps' whenever the solar cycle was at its peak. I am not aware of any such connection in the historical record.

Now none of this this argues against the theory that more CO2 means warmer temperatures on average. What is does argue against long established human tradition of attributing causes to what are random events. In less enlightened times the supernatural would be the cause - today it is pseudo science.

strawman? Is responding directly to your statement… a strawman? You offered a statement that has no particular relation to any previous posting. Your statement stands… and falls… on its own ridiculous paralleling. Again, your statement:

In the past weather was blamed on witches and demons. Today we have CO2. Nothing has changed except the superstitious have learned how to use pseudo scientific lingo to give their superstitions a veneer of respectability.

my reference to causal link pertains to your mentioning CO2; in the context of the OPs heatwave/extreme event reference, you’ve clearly drawn a parallel between superstition/witches & demons and those who recognize AGW climate change (and its CO2 causal association), as a link to the overall trend of increased frequency and/or intensity of extreme events, as attributed to AGW climate change. Again, per the OPs quoted NOAA rep, “It’s part of an overall trend”…

I will ask again:

would you care to substantiate your inferred claim that the sun is the causal link to the (relatively) recent warming?

[eyeball]

In the meantime...

June and 2010 are on track towards being the hottest on record.

[waldo]

you keep offering cursory, veiled innuendo-like references attempting to link science/scientists to political arguments, to politicization. C’mon man, spit it out… get it over with… get it off your chest. Cathartic and all that!

hey TimG... this is what actual climate change politicization looks like!

Ads Backed by Fossil-Fuel Interests Argue 'CO2 Is Green'

A group with ties to the fossil fuel industry launched a new ad campaign today pushing the idea that carbon dioxide isn't an environmental pollutant.

The organization "C02 is Green" funded a half-page advertisement in The Washington Post urging people to call their senators and seek a vote against "the president's cap-and-trade bill that will increase your cost of living and not change the climate.

"The bill is based on the false premise that man-made CO2 is a major cause of climate change," the ad says. "Real, empirical evidence indicates it is not."

The ad makes a number of other charges, including that the bill from Sens. John Kerry (D-Mass.) and Joe Lieberman (I-Conn.) will drive up prices for electricity, transportation fuel and food, that the country relies on fossil fuels and that the backers of the bill are "buying support from industries on Wall Street with various corporate giveaways."

CO2 is Green spokesman H. Leighton Steward sits on the board of directors of EOG Resources Inc., an oil and natural gas development company. He also is an honorary director at the industry trade group American Petroleum Institute, according to a biography on EOG's website.

"The ad reads like the 'climate deniers' manifesto,'" Di Martino said. "This Big Oil front group wants people to think Congress is going to raise taxes, kill jobs, spill more oil, take our children and charge us for the pleasure."

The ad, Di Martino said, is "funded by the world's largest polluters and those who stand to profit from our continued dependence on fossil fuels for our energy." In addition to Steward, he said, CO2 is Green is bankrolled by Corbin J. Robinson, chief executive of and leading shareholder in Natural Resource Partners, a Houston-based owner of coal resources.

[TimG]

as a link to the overall trend of increased frequency and/or intensity of extreme events, as attributed to AGW climate change.

I will make it very simple because you seem always miss the point:

- A claim that more CO2 leads gradually higher temps is well founded on science.

- A claim that more CO2 leads to stronger extremes is nothing but a medieval superstition.

It worth nothing that a heat wave/cold snaps is relative to a normal climate. So if Vancouver climate changes to become like LA then what we call a 'heat wave' today will be normal. This means it is completely irrational to claim that a warming climate will lead to more heat waves because the definition of heat wave will change as the climate warms.

The problem with AGW is not the science when properly stated with all of the uncertains and caveats. The problem are political activists that seek to make unfounded claims in order to support a political agenda.

Edited July 17, 2010 by TimG

[waldo]

my reference to causal link pertains to your mentioning CO2; in the context of the OPs heatwave/extreme event reference, you’ve clearly drawn a parallel between superstition/witches & demons and those who recognize AGW climate change (and its CO2 causal association), as a link to the overall trend of increased frequency and/or intensity of extreme events, as attributed to AGW climate change. Again, per the OPs quoted NOAA rep, “It’s part of an overall trend”…

I will make it very simple because you seem always miss the point:

- A claim that more CO2 leads gradually higher temps is well founded on science.

- A claim that more CO2 leads to stronger extremes is nothing but a medieval superstition.

uhhh... are you being purposely coy in choosing your "stronger" wording? Certainly, the question of intensity (versus frequency) is one that exists in arguments concerning hurricanes and AGW , but... heatwaves?

in any case, apparently, you would now choose to label the IPCC AR4 report as "medieval superstition" - oh my!

It is very likely that hot extremes, heat waves and heavy precipitation events will continue to become more frequent.

again... the probability attached to that IPCC 'very likely' likelihood assignment is: > 90% probability.

[TimG]

again... the probability attached to that IPCC 'very likely' likelihood assignment is:> 90% probability.

Oh Joy. Another alarmist money quote from the IPCC that leaves out critical context. For starters, the IPCC makes it clear as the average increases there will be more hot days (no kidding!). It does not provide any evidence to support the claim that excursions from the rising mean (i.e. heat waves) are increasing. Just a bunch of excuses about how the data is not good enough to show any such trend.

From the same document:

Widespread changes in extreme temperatures have been observed over the last 50 years. Cold days, cold nights and frost have become less frequent, while hot days, hot nights and heat waves have become more frequent

At this point, If you were intersted in the scientific facts you would agree with me that eyeball's claim of 'colder cold snaps' is pure nonsense.

Now if we wander over here we find:

Global studies of daily temperature and precipitation extremes over land (e.g., Frich et al., 2002; see also the TAR) suffer from both a scarcity of data and regions with missing data. The main reason is that in various parts of the globe there is a lack of homogeneous observational records with daily | resolution covering multiple decades that are part of integrated digitised data sets (GCOS, 2003). In addition, existing records are often inhomogeneous; for instance as a result of changes in observing practices or UHI effects (DeGaetano and Allen, 2002; Vincent et al., 2002; Wijngaard et al., 2003).

Gee, it looks like there is no conclusive evidence of a trend in extreme temperature events and UHI is part of the problem.

As for the poster boy of heat waves:

http://ije.oxfordjournals.org/cgi/content/short/37/2/309

Results During the 2006 heat wave (from 11 to 28 July), about 2065 excess deaths occurred in France. Considering the observed temperatures and with the hypothesis that heat-related mortality had not changed since 2003, 6452 excess deaths were predicted for the period. The observed mortality during the 2006 heat wave was thus markedly less than the expected mortality (4400 less deaths).

Conclusions The excess mortality during the 2006 heat wave, which was markedly lower than that predicted by the model, may be interpreted as a decrease in the population's vulnerability to heat, together with, since 2003, increased awareness of the risk related to extreme temperatures, preventive measures and the set-up of the warning system.

In other words, people adapt. Get over it. What we call a heat wave today will be nothing to remark about in 50 years. Edited July 17, 2010 by TimG

[bloodyminded]

In the past weather was blamed on witches and demons. Today we have CO2. Nothing has changed except the superstitious have learned how to use pseudo scientific lingo to give their superstitions a veneer of respectability.

I hope this is intended as wanton exaggeration for rhetorical effect.

[TimG]

I hope this is intended as wanton exaggeration for rhetorical effect.

It is and it is not. We live in a society where nothing bad can happen without it someone blaming it on climate change. I think the better question is: why are the people that insist on blaming everything on climate change any more rational than those that blamed bad things on witches and demons? After all, the 'scientific consensus' 1000 years ago was that witches and demons existed and they could cause bad things to happen. If we are really as rational as we claim to be we would stop trying to find causes for eveny random event and just accept that 's**t happens'. Edited July 17, 2010 by TimG

[bloodyminded]

It is and it is not. We live in a society where nothing bad can happen without it someone blaming it on climate change.

And again with the wild exaggerations; this is simply not true.

I think the better question is: why are the people that insist on blaming everything on climate change any more rational than those that blamed bad things on witches and demons? After all, the 'scientific consensus' 1000 years ago was that witches and demons existed and they could cause bad things to happen. If we are really as rational as we claim to be we would stop trying to find causes for event random event and just accept that 's**t happens'.

I very much appreciate the need for understanding that scientific error can be profound. But you can't compare "scientific consensus" of a thousand years ago to consensus today. Because a thousand years ago, science was a wholly different animal. It's not that it's tinkered with itself and become progressively better; it's that science, as we know it, did not exist.

The belief that witches and demons caused our problems was not based on anything we recognize as science; it was wholesale invention by religious authorities, and if anything has more in common with the current denial camp than with the climate scientists.

Aristotle believed that women had fewer teeth than men. This was not related in any way to "science": because science would insist we perform the radical experiment of counting women's teeth, a method that escaped Aristotle's notice.

Edited July 17, 2010 by bloodyminded

[TimG]

And again with the wild exaggerations; this is simply not true.

It is. See this link.

But you can't compare "scientific consensus" of a thousand years ago to consensus today. Because a thousand years ago, science was a wholly different animal.

There is a huge difference between science, as it is properly practiced, and science as it is perceived/used by the public at large. For most people science is simply the culture framework that explains the unknown.

The belief that witches and demons caused our problems was not based on anything we recognize as science; it was wholesale invention by religious authorities.

There is no evidence that the 'authorities' did not believe it themselves. The 'witches and demons' were a crude attempt to explain the world around and every human culture had variations on the theme. It is obviously flawed from our perspective today but that does not make it any less sincere and real.

This was not related in any way to "science": because science would insist we perform the radical experiment of counting women's teeth, a method that escaped Aristotle's notice.

No "we" don't. We rely on self annointed priests to tell us that they counted the teeth and priests who disagree with the 'consensus tooth count' are vilified and condemned as evil. Edited July 17, 2010 by TimG

[bloodyminded]

It is. See this link.

Now you're being coy.

Look, you can go through my posts--all of them, pick any one you like--and see me blaming something other than climate change for this or that catastrophe or injustice or error or mistake.

Then you can read your own posts, and discover the same thing.

Then you can pick any MLW member, read a few posts, and watch as they blame something other than climate change for any number of terrible things.

Which means--by definition, irrefutably, demonstrably, and uncontroversially--that your claim is not even an exaggeration, but is flatly and unequivocally untrue.

There is no evidence that the 'authorities' did not believe it themselves. The 'witches and demons' were a crude attempt to explain the world around and every human culture had variations on the theme. It is obviously flawed from our perspective today but that does not make it any less sincere and real.

It is also not science, as science did not exist.

No "we" don't. We rely on self annointed priests to tell us that they counted the teeth and priests who disagree with the 'consensus tooth count' are vilified and condemned as evil.

But that's not what happened. Your analogies are irrelevant and sidetracked at best.

Edited July 17, 2010 by bloodyminded

[TimG]

Which means--by definition, irrefutably, demonstrably, and uncontroversially--that your claim is not even an exaggeration, but is flatly and unequivocally untrue.

Fine. It was an exaggeration. Obviously 'all' bad thing are not blamed on climate change by everyone. But many absurd attributions are made on a regular basis.

It is also not science, as science did not exist.

It was a framework for explaining the world around people. Even science has evolved as a explanatory framework. It used to be that a theory that cannot be falsified is not science but some now some reject that and claim the 'consensus of experts' is sufficient. Edited July 17, 2010 by TimG

[waldo]

Now if we wander over here we find:

Global studies of daily temperature and precipitation extremes over land (e.g., Frich et al., 2002; see also the TAR) suffer from both a scarcity of data and regions with missing data. The main reason is that in various parts of the globe there is a lack of homogeneous observational records with daily | resolution covering multiple decades that are part of integrated digitised data sets (GCOS, 2003). In addition, existing records are often inhomogeneous; for instance as a result of changes in observing practices or UHI effects (DeGaetano and Allen, 2002; Vincent et al., 2002; Wijngaard et al., 2003).

Gee, it looks like there is no conclusive evidence of a trend in extreme temperature events and UHI is part of the problem.

interesting… when you don’t like something from an IPCC report, you’ll refer to it as, “Another alarmist money quote from the IPCC that leaves out critical context”, although you certainly have no problem in referencing an IPCC report when you presume it supports your position. The presumed context that you feel is somehow relevant, has you pulling out a global reference that speaks to an under-representation of spatial coverage. The IPCC claims concerning extreme events are always spoken of in terms of regional-scale changes. More specifically, the IPCC AR4 report clearly and categorically speaks to the degree of terrestrial surface area spatial coverage… as of AR4, “spatial coverage is now 71% of the terrestrial surface instead of 54% in the TAR, although tropical areas are still under-represented. Prior to 1950, insufficient data are available to develop global-scale maps of maximum and minimum temperature trends”. Your presumed “money quote”… is simply an acknowledgment of same.

again, per IPCC AR4: (Regional-scale changes include) - very likely increase in frequency of hot extremes, heat waves and heavy precipitation. And, again: the probability attached to that IPCC 'very likely' likelihood assignment is > 90% probability.

IPCC AR4 – Frequently Asked Questions:

FAQ 3.2 - Are Extreme Events, Like Heat Waves, Droughts or Floods, Expected to Change as the Earth’s Climate Changes?

Yes; the type, frequency and intensity of extreme events are expected to change as Earth’s climate changes, and these changes could occur even with relatively small mean climate changes. Changes in some types of extreme events have already been observed, for example, increases in the frequency and intensity of heat waves and heavy precipitation events.

In a warmer future climate, there will be an increased risk of more intense, more frequent and longer-lasting heat waves. The European heat wave of 2003 is an example of the type of extreme heat event lasting from several days to over a week that is likely to become more common in a warmer future climate. A related aspect of temperature extremes is that there is likely to be a decrease in the daily (diurnal) temperature range in most regions. It is also likely that a warmer future climate would have fewer frost days (i.e., nights where the temperature dips below freezing). Growing season length is related to number of frost days, and has been projected to increase as climate warms. There is likely to be a decline in the frequency of cold air outbreaks (i.e., periods of extreme cold lasting from several days to over a week) in NH winter in most areas. Exceptions could occur in areas with the smallest reductions of extreme cold in western North America, the North Atlantic and southern Europe and Asia due to atmospheric circulation changes.

In a warmer future climate, most Atmosphere-Ocean General Circulation Models project increased summer dryness and winter wetness in most parts of the northern middle and high latitudes. Summer dryness indicates a greater risk of drought. Along with the risk of drying, there is an increased chance of intense precipitation and flooding due to the greater water-holding capacity of a warmer atmosphere. This has already been observed and is projected to continue because in a warmer world, precipitation tends to be concentrated into more intense events, with longer periods of little precipitation in between. Therefore, intense and heavy downpours would be interspersed with longer relatively dry periods. Another aspect of these projected changes is that wet extremes are projected to become more severe in many areas where mean precipitation is expected to increase, and dry extremes are projected to become more severe in areas where mean precipitation is projected to decrease.

In concert with the results for increased extremes of intense precipitation, even if the wind strength of storms in a future climate did not change, there would be an increase in extreme rainfall intensity. In particular, over NH land, an increase in the likelihood of very wet winters is projected over much of central and northern Europe due to the increase in intense precipitation during storm events, suggesting an increased chance of flooding over Europe and other mid-latitude regions due to more intense rainfall and snowfall events producing more runoff. Similar results apply for summer precipitation, with implications for more flooding in the Asian monsoon region and other tropical areas. The increased risk of floods in a number of major river basins in a future warmer climate has been related to an increase in river discharge with an increased risk of future intense storm-related precipitation events and flooding. Some of these changes would be extensions of trends already underway.

There is evidence from modelling studies that future tropical cyclones could become more severe, with greater wind speeds and more intense precipitation. Studies suggest that such changes may already be underway; there are indications that the average number of Category 4 and 5 hurricanes per year has increased over the past 30 years. Some modelling studies have projected a decrease in the number of tropical cyclones globally due to the increased stability of the tropical troposphere in a warmer climate, characterised by fewer weak storms and greater numbers of intense storms. A number of modelling studies have also projected a general tendency for more intense but fewer storms outside the tropics, with a tendency towards more extreme wind events and higher ocean waves in several regions in association with those deepened cyclones. Models also project a poleward shift of storm tracks in both hemispheres by several degrees of latitude.

FAQ 3.3 - Has there been a Change in Extreme Events like Heat Waves, Droughts, Floods and Hurricanes?

Since 1950, the number of heat waves has increased and widespread increases have occurred in the numbers of warm nights. The extent of regions affected by droughts has also increased as precipitation over land has marginally decreased while evaporation has increased due to warmer conditions. Generally, numbers of heavy daily precipitation events that lead to flooding have increased, but not everywhere. Tropical storm and hurricane frequencies vary considerably from year to year, but evidence suggests substantial increases in intensity and duration since the 1970s. In the extratropics, variations in tracks and intensity of storms reflect variations in major features of the atmospheric circulation, such as the North Atlantic Oscillation.

In several regions of the world, indications of changes in various types of extreme climate events have been found. The extremes are commonly considered to be the values exceeded 1, 5 and 10% of the time (at one extreme) or 90, 95 and 99% of the time (at the other extreme). The warm nights or hot days (discussed below) are those exceeding the 90th percentile of temperature, while cold nights or days are those falling below the 10th percentile. Heavy precipitation is defined as daily amounts greater than the 95th (or for ‘very heavy’, the 99th) percentile.

In the last 50 years for the land areas sampled, there has been a significant decrease in the annual occurrence of cold nights and a significant increase in the annual occurrence of warm nights (Figure 1). Decreases in the occurrence of cold days and increases in hot days, while widespread, are generally less marked. The distributions of minimum and maximum temperatures have not only shifted to higher values, consistent with overall warming, but the cold extremes have warmed more than the warm extremes over the last 50 years (Figure 1). More warm extremes imply an increased frequency of heat waves. Further supporting indications include the observed trend towards fewer frost days associated with the average warming in most mid-latitude regions.

A prominent indication of a change in extremes is the observed evidence of increases in heavy precipitation events over the mid-latitudes in the last 50 years, even in places where mean precipitation amounts are not increasing . For very heavy precipitation events, increasing trends are reported as well, but results are available for few areas.

Drought is easier to measure because of its long duration. While there are numerous indices and metrics of drought, many studies use monthly precipitation totals and temperature averages combined into a measure called the Palmer Drought Severity Index (PDSI). The PDSI calculated from the middle of the 20th century shows a large drying trend over many Northern Hemisphere land areas since the mid-1950s, with widespread drying over much of southern Eurasia, northern Africa, Canada and Alaska, and an opposite trend in eastern North and South America. In the Southern Hemisphere, land surfaces were wet in the 1970s and relatively dry in the 1960s and 1990s, and there was a drying trend from 1974 to 1998. Longer-duration records for Europe for the whole of the 20th century indicate few significant trends. Decreases in precipitation over land since the 1950s are the likely main cause for the drying trends, although large surface warming during the last two to three decades has also likely contributed to the drying. One study shows that very dry land areas across the globe (defined as areas with a PDSI of less than –3.0) have more than doubled in extent since the 1970s, associated with an initial precipitation decrease over land related to the El Niño-Southern Oscillation and with subsequent increases primarily due to surface warming.

Changes in tropical storm and hurricane frequency and intensity are masked by large natural variability. The El Niño- Southern Oscillation greatly affects the location and activity of tropical storms around the world. Globally, estimates of the potential destructiveness of hurricanes show a substantial upward trend since the mid-1970s, with a trend towards longer storm duration and greater storm intensity, and the activity is strongly correlated with tropical sea surface temperature. These relationships have been reinforced by findings of a large increase in numbers and proportion of strong hurricanes globally since 1970 even as total numbers of cyclones and cyclone days decreased slightly in most basins. Specifically, the number of category 4 and 5 hurricanes increased by about 75% since 1970. The largest increases were in the North Pacific, Indian and Southwest Pacific Oceans. However, numbers of hurricanes in the North Atlantic have also been above normal in 9 of the last 11 years, culminating in the record-breaking 2005 season.

Based on a variety of measures at the surface and in the upper troposphere, it is likely that there has been a poleward shift as well as an increase in Northern Hemisphere winter storm track activity over the second half of the 20th century. These changes are part of variations that have occurred related to the North Atlantic Oscillation. Observations from 1979 to the mid-1990s reveal a tendency towards a stronger December to February circumpolar westerly atmospheric circulation throughout the troposphere and lower stratosphere, together with poleward displacements of jet streams and increased storm track activity. Observational evidence for changes in small-scale severe weather phenomena (such as tornadoes, hail and thunderstorms) is mostly local and too scattered to draw general conclusions; increases in many areas arise because of increased public awareness and improved efforts to collect reports of these phenomena.