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Did global warming stop in 1998? Jim Hansen says NO.

Inquiring minds might want to take a quick look at what Dr. James E. Hansen of the NASA Goddard Institute for Space Studies has to say:



The year 2007 tied for second warmest in the period of instrumental data, behind the record warmth of 2005, in the Goddard Institute for Space Studies (GISS) analysis. 2007 tied 1998, which had leapt a remarkable 0.2°C above the prior record with the help of the “El Nino of the century”. The unusual warmth in 2007 is noteworthy because it occurs at a time when solar irradiance is at a minimum and the equatorial Pacific Ocean is in the cool phase of its natural El Nino – La Nina cycle.


“Global warming stopped in 1998” has become a recent mantra of those who wish to deny the reality of human-caused global warming. The continued rapid increase of the five-year running mean temperature exposes this assertion as nonsense. In reality, global temperature jumped two standard deviations above the trend line in 1998 because the “El Nino of the century” coincided with the calendar year, but there has been no lessening of the underlying warming trend.


Solar irradiance will still be on or near its flat-bottomed minimum in 2008. Temperature tendency associated with the solar cycle, because of the Earth’s thermal inertia, has its minimum delayed by almost a quarter cycle, i.e., about two years. Thus solar change should not contribute significantly to temperature change in 2008.


La Nina cooling in the second half of 2007 (Figure 2) is about as intense as the regional cooling associated with any La Nina of the past half century, as shown by comparison to Plate 9 in Hansen et al. (http://pubs.giss.nasa.gov/docs/1999/1999_Hansen_etal.pdf) and updates to Plate 9 on the GISS web site. Effect of the current La Nina on global surface temperature is likely to continue for at least the first several months of 2008. Based on sequences of Pacific Ocean surface temperature patterns in Plate 9, a next El Nino in 2009 or 2010 is perhaps the most likely timing. But whatever year it occurs, it is a pretty safe bet that the next El Nino will help carry global temperature to a significantly higher level.


Competing with the short-term solar and La Nina cooling effects is the long-term global warming effect of human-made GHGs. The latter includes the trend toward less Arctic sea ice that markedly increases high latitude Northern Hemisphere temperatures. Although sea ice cover fluctuates from year to year, the large recent loss of thick multi-year ice implies that this warming effect at high latitudes should persist.


Based on these considerations, it is unlikely that 2008 will be a year with an unusual global temperature change, i.e., it is likely to remain close to the range of (high) values exhibited in 2002-2007. On the other hand, when the next El Nino occurs it is likely to carry global temperature to a significantly higher level than has occurred in recent centuries, probably higher than any year in recent millennia. Thus we suggest that, barring the unlikely event of a large volcanic eruption, a record global temperature clearly exceeding that of 2005 can be expected within the next 2-3 years.


In other words, despite cooling factors such as the ongoing La Nina and our position at the lowest point on the solar irradiation cycle, global temperatures remain high (and the five-year running average continues to climb) because of anthropogenic forcing factors, and unless there is a major volcanic eruption like Pinatubo in the new few years, we can expect that the next el Nino will bring new global high temperature records.


More here:  http://www.columbia.edu/~jeh1/mailings/20080114_GISTEMP.pdf

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