Modern Day Climate Change

I highly recommend watching the NSF video series linked above to get a very good overview of what the science is telling us about climate change. Then read on for the details.

Temperature Trends:

20 of the warmest years on record have occurred in the past 25 years. The warmest year globally was 2005 with the years 2009, 2007, 2006, 2003, 2002, and 1998 all tied for 2^nd within statistical certainty. (Hansen et al., 2010) The warmest decade has been the 2000s, and each of the past three decades has been warmer than the decade before and each set records at their end. The odds of this being a natural occurrence are estimated to be one in a billion! (Schmidt and Wolfe, 2009)

According to NOAA climate monitoring chief Deke Arndt (Romm, 2009):

The last 10 years are the warmest 10-year period of the modern record. Even if you analyze the trend during that 10 years, the trend is actually positive, which means warming.

Figure 7.1 (IPCC, 2007) shows the global mean temperature anomalies (compared to 1961-1990) from the years 1850 to 2005. Figure 7.1a (NCDC, 2010) shows the global mean temperature and CO₂ concentrations from the years 1880 to 2009. Of utmost concern is that the rate of warming has increased rapidly in the past few decades which means global warming is accelerating.

Figure 7.1: Global mean temperature anomalies (compared to 1961-1990) from the years 1850 to 2005

Figure 7.1a: Global mean temperatures and CO₂ concentration from 1880 to 2009

Figure 7.2 (Tamino, 2009) clearly shows that surface temperatures north of latitude 60^o are warming at an accelerated rate in the past few decades. Tamino (2009) retrieved 113 station records at latitude 60^oN or higher with at least 30 years of data.

Figure 7.2: Arctic surface temperatures since 1880.

Tamino (2009) explains here and here. The analyses show:

1. The Arctic has experienced a sudden, recent warming.
2. In the last decade extreme northern temperature has risen to unprecedented heights.
3. Over the last 3 decades, every individual station north of 70^o indicates warming, 13 of 17 are significant at 95% confidence, all estimated trend rates are faster than the global average, some are more than five times as fast.
4. Oft-repeated claims that “it was warmer in the 1930s” or “it was warmer in the 1940s” are wrong.
5. The idea that present arctic temperatures are about equal to their 1958 values is wrong.

Kauffman et al. (2009) also shows that the Arctic was experiencing long-term cooling in the past 2000 years according to Milankovitch cycles until very recently. Figure 7.3 reveals this trend shift:

Figure 7.3: Recent warming reverses long-term arctic cooling (Kaufmann et al. modified by University Corporation for Atmospheric Research)

Kaufmann et al. summarizes their study:

The temperature history of the first millennium C.E. is sparsely documented, especially in the Arctic. We present a synthesis of decadally resolved proxy temperature records from poleward of 60 ^oN covering the past 2000 years, which indicates that a pervasive cooling in progress 2000 years ago continued through the Middle Ages and into the Little Ice Age. A 2000-year transient climate simulation with the Community Climate System Model shows the same temperature sensitivity to changes in insolation as does our proxy reconstruction, supporting the inference that this long-term trend was caused by the steady orbitally driven reduction in summer insolation. The cooling trend was reversed during the 20th century, with four of the five warmest decades of our 2000-year-long reconstruction occurring between 1950 and 2000.

Arctic Ice & Glacial Trends:

Further signs of this warming trend can be seen in the Northern Hemisphere Sea Ice Extent from the National Snow and Ice Data Center. Figure 7.4 shows sea ice extent since 1953. For January 1953 through December 1979, data have been obtained from the UK Hadley Centre and are based on operational ice charts and other sources. For January 1979 through July 2009, data are derived from satellite. Figure 7.4a shows the most current sea ice extent from satellite measurements. Sea ice extent has been dramatically reduced since 1953.

Figure 7.4: Northern Hemisphere sea ice extent since 1953

Figure 7.4a: Current Northern Hemisphere sea ice extent from satellite measurements

Sea ice extent is just part of the picture. Sea ice thickness has also been measured by submarine and ICESat satellite measurement.

Figure 7.5 (Rothrock, et al., 1999) shows sea ice thickness has substantially declined. Using data from submarine cruises, Rothrock and collaborators determined that the mean ice draft at the end of the melt season in the Arctic has decreased by about 1.3 meters between the 1950s and the 1990s.

Figure 7.5: Mean sea ice draft: Decrease in Arctic sea ice draft for 1958 to 1997.

Since 2004 and there has been a dramatic decrease in thickness according to NASA's press release, NASA Satellite Reveals Dramatic Arctic Ice Thinning dated July, 2009. Some excerpts:

Using ICESat measurements, scientists found that overall Arctic sea ice thinned about 0.17 meters (7 inches) a year, for a total of 0.68 meters (2.2 feet) over four winters. The total area covered by the thicker, older "multi-year" ice that has survived one or more summers shrank by 42 percent.

In recent years, the amount of ice replaced in the winter has not been sufficient to offset summer ice losses. The result is more open water in summer, which then absorbs more heat, warming the ocean and further melting the ice. Between 2004 and 2008, multi-year ice cover shrank 1.54 million square kilometers (595,000 square miles) -- nearly the size of Alaska's land area.

During the study period, the relative contributions of the two ice types to the total volume of the Arctic's ice cover were reversed. In 2003, 62 percent of the Arctic's total ice volume was stored in multi-year ice, with 38 percent stored in first-year seasonal ice. By 2008, 68 percent of the total ice volume was first-year ice, with 32 percent multi-year ice.

Figure 7.5a: Northern Hemisphere sea ice thickness

Figure 7.5b: Northern Hemisphere sea ice thickness submarine & ICESAT combined

Figure 7.5b (Kwock & Rothrock, 2009) shows the mean thicknesses of six Arctic regions for the three periods (1958– 1976, 1993–1997, 2003–2007). Thicknesses have been seasonally adjusted to September 15. According to the authors:

"The overall mean winter thickness of 3.64 m in 1980 can be compared to a 1.89 m mean during the last winter of the ICESat record—an astonishing decrease of 1.75 m in thickness. Between 1975 and 2000, the steepest rate of decrease is 0.08 m/yr in 1990 compared to a slightly higher winter/summer rate of 0.10/0.20 m/yr in the five-year ICESat record (2003–2008). Prior to 1997, ice extent in the DRA was >90% during the summer minimum. This can be contrasted to the gradual decrease in the early 2000s followed by an abrupt drop to <55% during the record setting minimum in 2007. This combined analysis shows a long-term trend of sea ice thinning over submarine and ICESat records that span five decades."

Figure 7.5c: Current Arctic ice volume anomaly and trend from PIOMAS (Zhang, 2010)

Figure 7.5c above shows sea ice volume calculated using the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) developed at APL/PSC by Dr. J. Zhang and collaborators. Anomalies for each day are calculated relative to the average over the 1979 -2009 period for that day to remove the annual cycle. This image allows one to visualize recent variations of total Arctic Sea Ice Volume in the context of longer term variability. Daily sea ice volume anomalies for each day are computed relative to the 1979 to 2009 average for that day. The trend for the 1979 to present period is shown in blue. Shaded areas show one and two standard deviations from the trend.

	Fool Me Once: Artic Sea Ice is Just Fine Watch this video to see how Lord Monckton and other deniers are trying to fool you about sea ice.
	Peter Sinclair's Climate Crock of the Week: 2009 Sea Ice Update Watch this video to learn about the 2009 Arctic sea ice measurements.
	Peter Sinclair's Climate Crock of the Week: Ice Area vs. Volume Watch this video to learn about the difference between ice area and ice volume and why volume is more critical.

Velicogna (2009) used measurements from the GRACE (Gravity Recovery and Climate Experiment) satellite gravity mission to determine the ice mass-loss for the Greenland and Antarctic Ice Sheets during the period between April 2002 and February 2009. During this time period the mass loss of the ice sheets were accelerating with time implying that the ice sheets contribution to sea level becomes larger with time. In Greenland (Fig. 7.6), the mass loss increased from 137 Gt/yr in 2002–2003 to 286 Gt/yr in 2007–2009. In Antarctica (Fig. 7.7) the mass loss increased from 104 Gt/yr in 2002–2006 to 246 Gt/yr in 2006–2009.

Figure 7.6: Greenland Ice Mass Loss

Figure 7.7: Antarctic Ice Mass Loss

John Cook at Skeptical Science has several very good summaries of this research. See: An overview of Antarctic ice trends, An overview of Greenland ice trends, and Why is Greenland's ice loss accelerating?.

Glaciers also are used as a signature for climate change. Summer melting, called ablation, controls the mass and extent of glaciers. According to the World Glacier Monitoring Service (2009), preliminary mass balance values for the observation periods 2005/06 and 2006/07 have been reported from more than 100 and 80 glaciers worldwide, respectively. The mass balance data are calculated based on all reported values as well as on the data from the 30 reference glaciers in nine mountain ranges in North America and Europe with continuous observation series back to 1980.

The average mass balance of the glaciers with available long-term observation series around the world continues to decrease, with tentative figures indicating a further thickness reduction of 1.3 and 0.7 metres water equivalent (m w.e.) during the hydrological years 2006 and 2007, respectively. The new data continues the global trend in accelerated ice loss over the past few decades and brings the cumulative average thickness loss of the reference glaciers since 1980 at almost 11.3 m w.e. (see Figures 7.8 and 7.9).

Figure 7.8: Mean annual specific mass balance of reference glaciers

Figure 7.9: Mean cumulative specific mass balance of all reported glaciers (black line) and the reference glaciers (red line)

Glacial extent is also being monitored. Figure 7.10 (ibid) shows worldwide glacial extent measurements with red being a decrease and blue being an increase in the length of the glacier.

Figure 7.10: Glacial extent - retreating (red) and advancing (blue)

In 2005 there were 442 glaciers examined, 26 advancing, 18 stationary and 398 retreating. 90% of worldwide glaciers are retreating. In 2005, for the first time ever, no observed Swiss glaciers advanced. Of the 26 advancing glaciers, 15 were in New Zealand. Overall there has been a substantial volume loss of 11% of New Zealand glaciers from 1975-2005, but the number of advancing glacier is still significant. (ibid)

Ocean Heat Content:

Much of the heat that is delivered by the sun is stored in the Earth's oceans while only a fraction of this heat is stored in the atmosphere. Therefore, a change in the heat stored in the ocean is a better indicator of climate change than changes in atmospheric heat. Figures 7.11 and 7.12 (Richardson et al., 2009) and 7.13 (NODC, 2009) clearly show that the oceans have warmed significantly in recent years and the trend is 50% greater than that reported by the IPCC in 2007. The oceans are gaining heat much faster than other regions and more than half of the total heat change in the 42 years between 1961-2003 occurred in the last 10 years The oceans are gaining heat at an increasing rate.

Figure 7.11: Change in energy content in different components of the earth system for two periods: 1961-2003 (blue bars) and 1993-2003 (pink bars).

Figure 7.12: Change in ocean heat content since 1951.

Figure 7.13: Change in ocean heat content since 1955.

There have been a few published articles by Loehle (2009), Pielke (2008), and Willis (2008) that suggest ocean heat content trend since 2003 has either been flat or slightly negative. Of course, a few years does not a trend make but these results appear to be in conflict with the current upward trend. von Shuckmann, Gaillard, and Le Traon (2009) address this apparent conflict in their article Global hydrographic variability patterns during 2003–2008. Their data extends to 2000 m of ocean depth in contrast to Loehle (2009), Pielke (2008), and Willis (2008) data that only extends to 700 m. von Shuckmann, Gaillard, and Le Traon (2009) show that the heat content of the upper 500 m of ocean are subject to strong seasonal and interannual variations primarily due to salinity changes. However, when considering the heat content of the upper 2000 m of ocean, global mean heat content and height changes are clearly associated with a positive trend during the 6 years of measurements. Figure 7.14 (von Schuckmann et al., 2009) below shows this trend.

Figure 7.14: Change in global heat content for the uppermost 2000 m of ocean between 2003 and 2008

Murphy et al. (2009) examined the Earth's energy balance since 1950 including ocean heat content, radiative forcing by long-lived trace gases, and radiative forcing from volcanic eruptions. They considered the emission of energy by a warming Earth by using correlations between surface temperature and satellite data and show that the heat gained since 1950 is already quite significant. Their findings are illustrated below. (Cook, 2009)

Figure 7.15: Total Earth Heat Content from 1950 (ibid)

The oceans are taking in almost all of the excess heat since the 1970s which underscores the point that ocean heat content is a better indicator of global warming than atmospheric temperatures. Much of this ocean heat will be vented to the atmosphere in the future thus accelerating global warming.

Another way to illustrate where the heat is going is shown in Fig. 7.15a below:

Figure 7.15a: Components of global warming for the period 1993 to 2003 calculated from IPCC AR4 5.2.2.3 (Cook, 2010)

A superb discussion on this topic can be found at Skeptical Science's How we know global warming is still happening.

Precipitation Trends:

Figure 7.16 (IPCC, 2007) shows the Palmer Drought Severity Index (PDSI). The PDSI is a prominent index of drought. Red and orange areas are drier (-PDSI) than average and blue and green areas are wetter (+PDSI) than average. The smooth black curve shows decadal variations. The PDSI curve reveals widespread increasing African drought, especially in the Sahel. Note also the wetter areas, especially in eastern North and South America and northern Eurasia.

Figure 7.16: Palmer Drought Severity Index (PDSI)

Zhang et al. (2007), IPCC (2007), and Held and Soden (2006) conclude that global warming due to human activities is increasing the severity of drought in areas that already have drought and causing more rainfall in areas that are already wet.

Zhang et al. (2007) considered three groups of global climate model simulations and compared those simulations to the observed precipitation between 70^o north and 40^o south as shown in Figure 7.17 below.

• ANT denoted simulations included estimates of historical ANThropogenic (human) forcing only which included greenhouse gases and sulfate aerosols.
• NAT4 denoted simulations included just NATural external forcings only.
• ALL denoted simulations include BOTH of the above – natural and human forcing.

Figure 7.17: Observed precipitation vs. various simulations

This clearly shows that the ALL simulations (a and d) do a much better job of matching observed precipitation trends than either ANT (b and e) or NAT (c and f) alone. In fact, the correlations: ALL = 0.83, ANT = 0.69 and NAT4 = 0.02. It is for this reason that Zhang et al. (2007) conclude that changes in precipitation trends cannot be explained by natural forcing only and it certainly parallels what the IPCC WGI and WGII reports suggest.

Figure 7.18: Changes in observed vs. simulated precipitation anomalies (ibid)

Figure 7.18 shows that the models do not predict the mid-latitude trends at all. Regional precipitation pattern predictions are NOT a strong suit of the models which modelers have stated. What this image does show however, is that areas of green and yellow show where the model trends match those of the observed trends and the models do a decent job of forecasting the correct trends in most regions.

U.S. Climate Extremes Index (CEI):

The U.S. CEI is the arithmetic average of the following five or six# indicators of the percentage of the conterminous U.S. area:

1. The sum of (a) percentage of the United States with maximum temperatures much below normal and (b) percentage of the United States with maximum temperatures much above normal.
2. The sum of (a) percentage of the United States with minimum temperatures much below normal and (b) percentage of the United States with minimum temperatures much above normal.
3. The sum of (a) percentage of the United States in severe drought (equivalent to the lowest tenth percentile) based on the PDSI and (b) percentage of the United States with severe moisture surplus (equivalent to the highest tenth percentile) based on the PDSI.
4. Twice the value of the percentage of the United States with a much greater than normal proportion of precipitation derived from extreme (equivalent to the highest tenth percentile) 1-day precipitation events.
5. The sum of (a) percentage of the United States with a much greater than normal number of days with precipitation and (b) percentage of the United States with a much greater than normal number of days without precipitation.
6. * The sum of squares of U.S. landfalling tropical storm and hurricane wind velocities scaled to the mean of the first five indicators.

# The sixth indicator is experimental and is included in the experimental version of the CEI.
* The sixth indicator is only utilized when the period of interest includes months with significant tropical activity. For practical purposes, the CEI does not include the sixth indicator for the cold season (Oct-Mar), winter (Dec-Feb) or spring (Mar-May). It also cannot be calculated independent of the first five indicators. (Gleason, 2009)

Figure 7.19 (ibid) shows that in the United States, extremes in climate are on the increase since 1970.

Figure 7.19: United States Climate Extremes Index

According to Stanford University scientists Diffenbaugh and Ashfaq (2010):

"In the next 30 years, we could see an increase in heat waves like the one now occurring in the eastern United States or the kind that swept across Europe in 2003 that caused tens of thousands of fatalities. Those kinds of severe heat events also put enormous stress on major crops like corn, soybean, cotton and wine grapes, causing a significant reduction in yields."

According to the climate models, an intense heat wave – equal to the longest on record from 1951 to 1999 – is likely to occur as many as five times between 2020 and 2029 over areas of the western and central United States. The 2030s are projected to be even hotter. "Occurrence of the longest historical heat wave further intensifies in the 2030-2039 period, including greater than five occurrences per decade over much of the western U.S. and greater than three exceedences per decade over much of the eastern U.S.," the authors wrote.

Figure 7.19a: Number of Extremely Hot Seasons Per Decade in the US

The authors also forecast a dramatic spike in extreme seasonal temperatures during the current decade. Temperatures equaling the hottest season on record from 1951 to 1999 could occur four times between now and 2019 over much of the United States. The 2020s and 2030s could be even hotter, particularly in the American West. From 2030 to 2039, most areas of Utah, Colorado, Arizona and New Mexico could endure at least seven seasons equally as intense as the hottest season ever recorded between 1951 and 1999. The authors also determined that the hottest daily temperatures of the year from 1980 to 1999 are likely to occur at least twice as often across much of the United States during the decade of the 2030s (Shwartz, 2010).

The United States is not alone. Severe weather is increasing globally evidenced most recently by severe heat in Russia and flooding in Pakistan, among others, that have been strongly linked to climate change.

Are These Trends Unusual?:

They are unprecedented in the modern record!

• The concentration of CO₂ has reached a record high relative to the past 15 million years and has done so at an exceptionally fast rate.
• Most of the warming in the past 50 years is attributable to human activities.
• CO₂ concentrations are known accurately for the past 650,000 years. During that time, they varied between 180 ppm and 300 ppm. As of March 2009 CO₂ is 385 ppm which took about 100 years to increase. For comparison, it took over 5,000 years for an 80 ppm rise after the last ice age.
• Higher values than today have only occurred over many millions of years.
• The last time CO₂ levels were this high, sea level was 25 to 40 meters higher than present day.
• Although large climate changes have occurred in the past, there is no evidence that they took place at a faster rate than the present warming.
• If projections of a 5 ^oC warming in this century are realized, Earth will have experienced the same amount of global warming as it did at the end of the last glacial maximum.
• There is no evidence that this rate is matched to a comparable global temperature increase over the last 50 million years!

Sea-Level Rise:

Sea-level rise due to global warming is a serious threat, especially to coastal communities in developing countries. Sea level gradually rose in the 20th century and is currently rising at an increased rate, after a period of little change between AD 0 and AD 1900. Sea level is predicted to rise at an even greater rate in this century, with 20th century estimates of 1.7 mm per year (IPCC, 2007). When climate warms, ice on land melts and flows back into the oceans raising sea levels. Also, when the oceans warm, the water expands (thermal expansion) which raises sea levels. Figure 7.20 (IPCC, 2007) shows the projected sea-level rise through AD 2100.

Figure 7.20: Projected sea-level rise through AD 2100

Figure 7.21 (Richardson et al., 2009) shows that IPCC 1990 projected sea level increases were too conservative. The latest observations show that sea levels have risen faster than previous projections.

Figure 7.21: Observed sea-level rise between 1970 and 2008 compared to IPCC projections

According to The Copenhagen Diagnosis (2009):

"Satellites show great global average sea-level rise (3.4 mm/yr over the past 15 years) to be 80% above past IPCC predictions. This acceleration in sea-level rise is consistent with a doubling in contribution from melting of glaciers, ice caps and the Greenland and West-Antarctic ice-sheets. By 2100, global sea-level is likely to rise at least twice as much as projected by Working Group 1 of the IPCC AR4, for unmitigated emissions it may well exceed 1 meter. The upper limit has been estimated as 2 meters sea-level rise by 2100. Sea-level will continue to rise for centuries after global temperature have been stabilized and several meters of sea level rise must be expected over the next few centuries."

Figure 7.21a (Colorado Center for Astrodynamics Research) shows the current sea level change data using seasonally adjusted values from TOPEX and Jason while figure 7.21b (Sato & Hansen, 2010) shows mean sea level rise over the past 140 years.

Figure 7.21a: Current measured sea level change

Figure 7.21b: Sea level rise since 1870.

Mazria & Kirshner (2005) in Nation Under Siege: Sea Level Rise at Our Doorstep, a coastal impact study, show that beginning with just one meter of sea level rise, US cities would be physically under siege, with calamitous and destabilizing consequences. One can view the impact of sea level rise of various US cities at their interactive Website. An example is shown below for Miami Beach, FL today (Fig. 7.21c) vs. in the year 2100 (Fig. 7.21d) with a 1 meter sea level rise.

Figure 7.21c: Miami Beach today

Figure 7.21d: Miami Beach in 2100 with a 1 m sea level rise

Lemonick (2010) writes in the article The Secret of Sea Level Rise: It Will Vary Greatly by Region:

As the world warms, sea levels could easily rise three to six feet this century. But increases will vary widely by region, with prevailing winds, powerful ocean currents, and even the gravitational pull of the polar ice sheets determining whether some coastal areas will be inundated while others stay dry.

Hanson et al. (2008) believe that it is quite possible Earth could end up ice free with CO₂ levels of 350 ppm which is well below where we currently are. Because the melting of Antarctic ice takes centuries there is time to lower the "tipping point" level of CO₂ before it is too late. When Antarctica was last ice-free, sea levels were 70m (~230 feet) higher than today.

Climate Change and Hurricanes:

A recent paper published by some of the top hurricane researchers in the field (Knutson, et al. 2010) concludes:

...future projections based on theory and high-resolution dynamical models consistently indicate that greenhouse warming will cause the globally averaged intensity of tropical cyclones to shift towards stronger storms, with intensity increases of 2–11% by 2100. Existing modelling studies also consistently project decreases in the globally averaged frequency of tropical cyclones, by 6–34%. Balanced against this, higher resolution modelling studies typically project substantial increases in the frequency of the most intense cyclones, and increases of the order of 20% in the precipitation rate within 100 km of the storm centre.

There has been an observed increase in tropical cyclones (TC) since the mid-1990s. Warmer oceans have played a significant role in this increased frequency. A new study by Emanuel (2010) suggests that lower stratospheric cooling may also be responsible for the uptick in activity and intensity. Climate models may be underestimating future hurricane frequency and intensity because they do not appear to include the impact of stratospheric cooling. Emanuel's research suggests that there may be more hurricanes in the future despite the current consensus of a 6–34% decrease in frequency.

By 2100, the climate is expected to warm 5 ^oC to 6 ^oC or more above pre-IR values. During the Pliocene, about 2.5 to 5 million years ago, CO₂ levels were comparable to today's levels (near 400 ppm) and the climate was about 3 ^oC to 5 ^oC warmer than pre-IR. Geographically, the Earth was also very similar to today so the Pliocene offers a glimpse of what the world may look like by the year 2100. Federov, Brierley, & Emanuel (2010) modeled the expected TC activity in the early Pliocene world. Fig. 7.21e (Ibid) is a comparison of modern TC activity (a) and that of the Pliocene (b). This image is a sobering look at what may lie ahead in our world by 2100.

Figure 7.21e: Tracks and intensity of modern tropical cyclones (a) and during early Pliocene (b).

Vechi, Swanson, and Soden (2008) conclude that predicting the future of hurricane activity is at a crossroads. Vechi et al. compared the observed relation of the power dissipation index (PDI) vs. sea-surface temperatures (SST) in the main development region of Atlantic hurricanes. (PDI is the cube of the instantaneous tropical cyclone wind speed integrated over the life of all storms in a given season; more intense and frequent basinwide hurricane activity lead to higher PDI values.) There are two very different futures depending on whether absolute SST or relative SST controls PDI.

Figure 7.22 (ibid) shows PDI anomalies based on absolute SST.

Figure 7.22: PDI anomalies based on absolute SST

By 2100, the lower end of the model projections shows a PDI comparable to that of 2005, when four major hurricanes (sustained winds of over 100 knots) struck the continental United States, causing more than $100 billion in damage. The upper end of the projections exceeds 2005 levels by more than a factor of two. Combined with rising sea levels, coastal communities face a bleak future if absolute SST determines hurricane activity and strength.

Figure 7.23 (ibid) shows PDI anomalies based on "relative SST" which is the SST in the tropical Atlantic main development region relative to the tropical mean SST.

Figure 7.23: PDI anomalies based on relative SST

A future where relative SST controls Atlantic hurricane activity is a future similar to the recent past, with periods of higher and lower hurricane activity relative to present-day conditions due to natural climate variability, but with little long-term trend. Even in this scenario, rising sea levels will still allow hurricanes to do more damage in the future than in present day.

Because the correlation of PDI vs. absolute SST and PDI vs. relative SST are equivalent, Vechi et al. conclude that more research is needed in this area.

Realclimate's Atlantic Tropical Cyclone Records – Trends and Ephemerality (June, 2010) is a very good synopsis of what is known and not known about climate change and tropical cyclone projections.

IGBP Climate-Change Index:

Figure 7.24: IGBP Climate-Change Index (Click for larger image)

The IGBP Climate-Change Index brings together key indicators of global change: atmospheric carbon dioxide, temperature, sea level and sea ice. It will be released annually. The index gives an annual snapshot of how the planet's complex systems - the ice, the oceans, the land surface and the atmosphere - are responding to the changing climate. The index rises steadily from 1980 - the earliest date the index has been calculated. The change is unequivocal, it is global, and it is in one direction - up!

Each parameter is normalized between -100 and +100. Zero is no annual change. One hundred is the maximum-recorded annual change since 1980. The normalised parameters are averaged. This gives the index for the year. The value for each year is added to that of the previous year to show the cumulative effect of annual change. (IGBP Climate-Change Index, 2010)

What if Humans Decrease Emissions?:

According to the IPCC (2007):

• Some concentrations decline almost immediately while others still increase for centuries.
• About 45% of CO₂ is removed by oceans and the biosphere but 20% remains for thousands of years.
• Therefore, CO₂ concentrations will continue to increase in the long term even if they are reduced today.
• Only a complete shut-off of CO₂ emissions would result in a long-term stabilization at a constant level.
• Cutting CO₂ emissions by 50% today will only stabilize the levels for the next 10 years.

Next: The Global Warming Denial Machine

• Introduction
• The Scientific Consensus
• Determining the Climate Record
• Impact of Greenhouse Gases
• Climate Change: The Smoking Gun for Humans
• Natural Causes of Climate Change
• Global Cooling?
• Climate Models & Accuracy
• The Global Warming Denial Machine
• Global Warming Misinformation
• Reasons for the Misinformation
• How to Talk to a Conservative about Climate Change
• Summary of Key Points
• Suggested Reading
• Works Cited

Last updated: 08/26/10