JC's view conflicts sharply with the alarmist statements you hear from the media, politicians, and many "climate scientists". I have put the latter in quotes because so many of them have no credible reason for their alarmist position; hence are not scientists in the true sense.
Some excerpts from JC's paper follow.
-----------------------------------
Executive summary
This Report assesses the scientific basis for projections of future hurricane activity. The Report evaluates the assessments and projections from the Intergovernmental Panel on Climate Change (IPCC) and recent national assessments regarding hurricanes. The uncertainties and challenges at the knowledge frontier are assessed in the context of recent research, particularly with regards to natural variability. The following four questions frame this Report:
1 Is recent hurricane activity unusual?
In the North Atlantic, all measures of hurricane activity have increased since 1970, although comparably high levels of activity also occurred during the 1950’s and 1960’s. Geologic evidence indicates that the current heightened activity in the North Atlantic is not unusual, with a ‘hyperactive period’ apparently occurring from 3400 to 1000 years before present. Prior to the satellite era (1970’s), there are no reliable statistics on global hurricane activity. Global hurricane activity since 1970 shows no significant trends in overall frequency, although there is some evidence of a small increase in the number of major hurricanes.
2 Have hurricanes been worsened by man-made global warming?
Any recent signal of increased hurricane activity has not risen above the background variability of natural climate variations. At this point, there is no convincing evidence that man-made global warming has caused a change in hurricane activity.
3. Have hurricane landfall impacts been worsened by man-made global warming?
Of recent impactful U.S. land-falling hurricanes, only the rainfall in Hurricane Harvey is unusual in context of the historical record. Warmer sea surface temperatures are expected to contribute to an overall increase in hurricane rainfall, although hurricane induced rainfall and flooding is dominated by natural climate variability. Storm surge risk is increasing slightly owing to the slow creep of sea level rise. The extent to which the recent increase in ocean temperatures and sea level rise can be attributed to man-made global warming is disputed. The primary driver for increased economic losses from land-falling hurricanes is the massive population buildup along coastlines.
4. How will hurricane activity change during the 21st century?
Recent assessment reports have concluded that there is low confidence in projections of future changes to hurricane activity. Any projected change in hurricane activity is expected to be small relative to the magnitude of natural variability in hurricane activity.
----------
Over the years, the way that hurricanes have been observed has changed radically. As a result, many hurricanes are now recorded that would have been missed in the past. Furthermore, satellites are now able to continually assess wind speeds, thus recording peak wind speeds that may have been missed in pre-satellite days. Unfortunately, temporally inconsistent and potentially unreliable global historical data hinder detection of trends in tropical cyclone activity. ----------
While an increase in hurricane intensity has long been hypothesized to occur as global sea surface temperatures increase, identification of any significant trend in the hurricane data is hampered by a short data record and substantial natural variability.
----------
A positive rate of hurricane intensification has been identified in recent decades in the Atlantic. Whether this trend is associated with natural variability or warming is unknown. Global data on rates of hurricane intensification is ambiguous.
----------
In recent decades, the Northern Hemisphere Pacific Ocean has seen a poleward migration in hurricane track location and location of maximum intensity, and also a slowing of hurricane motion. This migration has been attributed primarily to natural variability of the ocean circulations.
----------
Outside the North Atlantic, and particularly in the Southern Hemisphere, the historical data sets are fairly meager and of questionable quality, particularly with regards to intensity. There is no evidence of trends that exceeds natural variability.
----------
All measures of Atlantic hurricane activity show a significant increase since 1970. However, high values of hurricane activity (comparable to the past two decades) were also observed during the 1950’s and 1960’s, and by some measures also in the late 1920’s and 1930’s.
----------
There has not been a timeline or synthesis of the Atlantic hurricane paleotempestology results for the past five thousand years, either regionally or for the entire coastal region. However, it is clear from these analyses that significant variability of landfall probabilities occurs on century to millennial time scales. There appears to have been a broad hyperactive period from 3400 to 1000 years B.P. High activity persisted in the 26 Gulf of Mexico until 1400 AD, with a shift to more frequent severe hurricane strikes from the Bahamas to New England occurring between 1400 and 1675 AD. Since 1760, there was a gradual decline in activity until the 1990’s.
----------
3.5 ConclusionsAnalyses of both global and regional variability and trends of hurricane activity provide the basis for detecting changes and understanding their causes.
The relatively short historical record of hurricane activity, and the even shorter record from the satellite era, is not sufficient to assess whether recent hurricane activity is unusual for the current interglacial period. Results from paleotempestology analyses in the North Atlantic at a limited number of locations indicate that the current heightened activity is not unusual, with a hyperactive period apparently occurring from 3400 to 1000 years before present.
Global hurricane activity since 1970 shows no significant trends in overall frequency. There is some evidence of increasing numbers of major hurricanes and of an increase in the percentage of Category 4 and 5 hurricanes, although the quality of intensity data in some regions prior to 1988 is disputed.
In the North Atlantic, all measures of hurricane activity have increased since 1970, although comparably high levels of activities also occurred during the 1950’s and 1960’s.
----------
The observational database (since 1970 or even 1850) is too short to assess the full impact of natural internal variability associated with large-scale ocean circulations. Paleotempestology analyses indicate that recent hurricane activity is not unusual. Given the limited data record and its quality, there is no evidence of any changes in global or regional hurricane activity that exceeds natural variability.
----------
With regards to the observed global warming of the oceans, it is clear that manmade contributions to atmospheric CO2 do not provide a complete explanation of this warming. Solar variations, volcanic eruptions and the large-scale ocean circulation patterns also have a substantial influence on temperature variations in the global oceans.
----------
Atlantic hurricane processes are influenced substantially by the natural modes of ocean circulation variability in the Atlantic, notably the Atlantic Multidecadal Oscillation and the Atlantic Meridional Mode.
----------
Hurricanes in the Atlantic and Pacific are influenced substantially by the natural modes of ocean circulation variability in the Pacific. These modes include ENSO and Modoki, and also the Pacific Decadal Oscillation and the North Pacific Gyre Oscillation.
----------
Global climate models are currently of limited use in hurricane attribution studies. High-resolution models used to simulate individual hurricanes are being used to perform controlled experiments that focus on specific events and the complexities of relevant physical processes. However, definitive conclusions regarding the impact of man-made warming on hurricanes cannot be determined from these simulations, given the current state of model development and technology.
----------
In summary, there is no observed trend in hurricane activity that has risen above the background variability of natural processes. It is possible that man-made climate change may have caused changes in hurricane activity that are not yet detectable due to the small magnitude of these changes compared to estimated natural variability, or due to observational limitations. But at this point, there is no convincing evidence that man-made global warming has caused a change in hurricane activity.
----------
U.S. land-falling hurricanes show substantial year-to-year and decadal variability, associated primarily with ENSO and the Atlantic Multi-decadal Oscillation. Over the last century, there is a slight overall negative trend in the total number of hurricanes and major hurricanes striking the U.S. The number of major hurricanes striking the U.S. in recent decades is lower than the 1930’s, 1940’s and 1950’s. During the period 2006-2016, no major hurricanes struck the continental U.S.
----------
No trend in Caribbean landfalls has been observed. ENSO and Atlantic Multidecadal Oscillation dominate the variability of Caribbean landfalls. Historical records show that the time span 1968–1977 was probably the most inactive period since the islands were settled in the 1620s and 1630s.
----------
There are substantial challenges in constructing a homogeneous global hurricane landfall data set. Since 1970, the global frequency of total and major hurricane landfalls shows considerable interannual variability, but no significant linear trend. There is substantial regional variability in hurricane landfalls, primarily associated with ENSO phase.
----------
Examination of the number and intensity of historical Texas land-falling hurricanes shows no relationship with surface temperatures in the Gulf of Mexico. Harvey’s extreme rainfall has been linked to unusually high temperatures in the Gulf of Mexico that were associated primarily with local ocean circulation patterns. It has been estimated that at most about 2 inches of Hurricane Harvey’s peak amount of 60 inches can be linked with man-made global warming.
----------
Hurricane Irma set several intensity records, although these have not been linked in any way to sea surface temperature or man-made global warming. Historical data of Florida land-falling major hurricanes indicate no trends in either frequency or intensity.
----------
Of the four hurricanes considered here, only the rainfall in Hurricane Harvey passes the detection test, given that it is an event unprecedented in the historical record for a continental U.S. landfalling hurricane. Arguments attributing the high levels of rainfall to near record ocean heat content in the western Gulf of Mexico are physically plausible. The extent to which the high value of ocean heat content in the western Gulf of Mexico can be attributed to manmade global warming is debated. Owing to the large interannual and decadal variability in the Gulf of Mexico (e.g. ENSO), it is not clear that a dominant contribution from manmade warming can be identified against the background internal climate variability.
----------
The climate model projections of 21st century surface temperature and sea level rise are contingent on the following assumptions [IPCC AR5 WG1 Section12.2.3]: 1. Emissions follow the specified concentration pathways (RCP). 2. Climate models accurately predict the amount of warming in 21st century. 3. Solar variability follows that of the late 20th century, which coincided with a Grand Solar Maximum. 4. Natural internal variability of ocean circulations does not impact temperature or sea level rise on these timescales. 5. Major volcanic eruptions are not considered. Each of these contingent assumptions, with the possible exception of natural internal variability, likely contributes to a warm bias in the 21st century climate model projections.
----------
On timescales at least to 2050, variations in hurricane activity are expected to be dominated by natural variability, relative to any secular warming trends. A forthcoming shift to the cold phase of the Atlantic Multidecadal Oscillation – on a time scale of a decade or so – would result in fewer major hurricanes, lower values of Accumulated Cyclone Energy and fewer landfalls striking Florida, the U.S. east coast and the Caribbean. At some point in the coming decades, we can also anticipate a shift in the Pacific Decadal Oscillation towards more frequent La Niña events, which are associated with more activity in the Atlantic but suppressed activity in the Pacific.
----------
8. Conclusions
Numerous assessments and reviews have been conducted of the possible role of manmade global warming on global and regional hurricane activity. Overall, the ‘consensus’ among scientists on the possible role of manmade global warming on hurricane activity has been essentially unchanged over the past 15 years.
This Special Report on Hurricanes and Climate Change is distinguished from recent assessments by a focus on hurricane aspects that contribute to landfall impacts, and an increased emphasis on paleotempestology and interpretation of natural variability. Arguments have been presented supporting the important and even dominant role that natural processes play in global and regional hurricane variations and change.
1. Is recent hurricane activity unusual? In the North Atlantic, all measures of hurricane activity have increased since 1970, although comparably high levels of activity also occurred during the 1950’s and 1960’s. Geologic evidence indicates that the current heightened activity in the North Atlantic is not unusual, with a hyperactive period apparently occurring from 3400 to 1000 years before present. Prior to the satellite era (1970’s), there are no reliable statistics on global hurricane activity. Global hurricane activity since 1970 shows no significant trends in overall frequency, although there is some evidence of increasing numbers of major hurricanes.
This Special Report on Hurricanes and Climate Change is distinguished from recent assessments by a focus on hurricane aspects that contribute to landfall impacts, and an increased emphasis on paleotempestology and interpretation of natural variability. Arguments have been presented supporting the important and even dominant role that natural processes play in global and regional hurricane variations and change.
1. Is recent hurricane activity unusual? In the North Atlantic, all measures of hurricane activity have increased since 1970, although comparably high levels of activity also occurred during the 1950’s and 1960’s. Geologic evidence indicates that the current heightened activity in the North Atlantic is not unusual, with a hyperactive period apparently occurring from 3400 to 1000 years before present. Prior to the satellite era (1970’s), there are no reliable statistics on global hurricane activity. Global hurricane activity since 1970 shows no significant trends in overall frequency, although there is some evidence of increasing numbers of major hurricanes.
2. Have hurricanes worsened from man-made global warming?
Models and theory suggest that hurricane intensity and rainfall should increase in a warming climate. Convincing attribution of any changes to man-made global warming requires that a change in hurricane characteristics be identified from observations, with the change exceeding natural variability.
Any signal of recent increased hurricane activity has not risen above the background variability of natural climate variations. At this point, there is no convincing evidence that man-made global warming has caused a change in hurricane activity.
While there is much physically-plausible speculation among scientists regarding impacts of global warming on hurricanes, most of this speculation has weak justification when the observational record is examined in context of natural climate variability.
3. Have hurricane landfall impacts been worsened by man-made global warming?
Worldwide economic losses from landfalling tropical cyclones have increased in recent decades. In addition to the frequency and intensity of landfalling hurricanes, the following variables contribute to damage: horizontal size of the hurricane, forward speed of motion near the coast, storm surge and rainfall.
Of the recent impactful U.S. landfalling hurricanes, only the rainfall in Hurricane Harvey is unusual in context of the historical record of U.S. landfalling hurricanes. Warmer sea surface temperatures are expected to contribute to an overall increase in hurricane rainfall, although hurricane-induced rainfall and flooding is dominated by natural climate variability. Storm surge risk is increasing owing to the slow creep of sea level rise. The extent to which the recent increase in ocean temperatures and sea level rise can be attributed to man-made global warming is disputed. The primary driver for increased economic losses from landfalling hurricanes is the massive population buildup along the coasts.
4. How will hurricane activity change during the 21st century?
Recent assessment reports have concluded that there is low confidence in projections of future changes to hurricane activity. Any projected change in hurricane activity is expected to be small relative to the magnitude of natural variability in hurricane activity.
Decadal variability of hurricane activity is expected to provide much greater variability than the signal from global warming. In particular, a shift to the cold phase of Atlantic Multidecadal Oscillation (AMO) is anticipated within the next 15 years. All other things being equal (such as the frequency of El Niño and La Niña events), the cold phase of AMO harkens reduced Atlantic hurricane activity and fewer landfalls for Florida, the east coast and the Caribbean.
Substantial advances have been made in recent years in the ability of climate models to simulate the variability of hurricanes. However, inconsistent hurricane projections have emerged from modeling studies. Progress continues to be made, particularly with models that are coupled to the ocean. Apart from the challenges of simulating hurricanes in climate models, the amount of warming projected by climate models for the 21st century is associated with deep uncertainty. Hence, projections of future hurricane activity are contingent on the amount of predicted global warming being correct.
No comments:
Post a Comment