NASA’s Goddard Institute for Space Studies has released its final report on “2008 Global Temperatures.” Last year “was the coolest year since 2000.” Given 0.05°C “uncertainty in comparing recent years,” NASA “can only conclude with confidence that 2008 was somewhere within the range from 7th to 10th warmest year in the record.”

The bigger climate news, of course, is that “in the period of instrumental measurements, which extends back to 1880 … The ten warmest years all occur within the 12-year period 1997-2008.” That’s why the climate story of the decade is that the 2000s are on track to be nearly 0.2°C warmer than the 1990s. And that temperature jump is especially worrisome since the 1990s were only 0.14°C warmer than the 1980s.

The headline coming out of NASA’s report, however, is clearly that they are sticking by their near-term forecast of an imminent record:

Finally, in response to popular demand, we comment on the likelihood of a near-term global temperature record. Specifically, the question has been asked whether the relatively cool 2008 alters the expectation we expressed in last year’s summary that a new global record was likely within the next 2-3 years (now the next 1-2 years).

Since global temperature in any year can be affected by many factors that have nothing to do with the long-term climate trend, and since short-term predictions gone awry are inevitably seized on by the DICKs (denier-industrial-complex kooks) as evidence the long-term predictions are wrong (even though they are no such thing), I’m not sure it is wise for GISS to make such predictions. But they have made the prediction:

Given our expectation of the next El Niño beginning in 2009 or 2010, it still seems likely that a new global temperature record will be set within the next 1-2 years, despite the moderate negative effect of the reduced solar irradiance.

Their analysis is certainly worth reviewing since, for better or worse, what happens to temperatures in the next few years may well affect just how much climate action that we are going to take (I will discuss the medium-term temperature forecast in the literature at the end):

Natural dynamical variability: The largest contribution is the Southern Oscillation, the El Niño-La Niña cycle. The Niño 3.4 temperature anomaly (the bottom line in the top panel of Fig. 2), suggests that the La Niña may be almost over, but the anomaly fell back (cooled) to -0.7°C last month (December). It is conceivable that this tropical cycle could dip back into a strong La Niña, as happened, e.g., in 1975. However, for the tropical Pacific to stay in that mode for both 2009 and 2010 would require a longer La Niña phase than has existed in the past half century, so it is unlikely. Indeed, subsurface and surface tropical ocean temperatures suggest that the system is “recharged”, i.e., poised, for the next El Niño, so there is a good chance that one may occur in 2009. Global temperature anomalies tend to lag tropical anomalies by 3-6 months.

Solar irradiance: The solar output remains low (Fig. 4, below), at the lowest level in the period since satellite measurements began in the late 1970s, and the time since the prior solar minimum is already 12 years, two years longer than the prior two cycles. This has led some people to speculate that we may be entering a “Maunder Minimum” situation, a period of reduced irradiance that could last for decades. Most solar physicists expect the irradiance to begin to pick up in the next several months — there are indications, from the polarity of the few recent sunspots, that the new cycle is beginning.

Figure 4. Solar irradiance through November 2008 from Frohlich and Lean [ref. 8]. (Click for large GIF.)

solar irradiance

However, let’s assume that the solar irradiance does not recover. In that case, the negative forcing, relative to the mean solar irradiance is equivalent to seven years of CO2 increase at current growth rates. So do not look for a new “Little Ice Age” in any case. Assuming that the solar irradiance begins to recover this year, as expected, there is still some effect on the likelihood of a near-term global temperature record due to the unusually prolonged solar minimum. Because of the large thermal inertia of the ocean, the surface temperature response to the 10-12 year solar cycle lags the irradiance variation by 1-2 years. Thus, relative to the mean, i.e, the hypothetical case in which the sun had a constant average irradiance, actual solar irradiance will continue to provide a negative anomaly for the next 2-3 years.Volcanic aerosols: Colorful sunsets the past several months suggest a non-negligible stratospheric aerosol amount at northern latitudes. Unfortunately, as noted in the 2008 Bjerknes Lecture [ref. 9], the instrument capable of precise measurements of aerosol optical depth depth (SAGE, the Stratospheric Aerosol and Gas Experiment) is sitting on a shelf at Langley Research Center. Stratospheric aerosol amounts are estimated from crude measurements to be moderate. The aerosols from an Aleutian volcano, which is thought to be the primary source, are at relatively low altitude and high latitudes, where they should be mostly flushed out this winter. Their effect in the next two years should be negligible.

Greenhouse gases: Annual growth rate of climate forcing by long-lived greenhouse gases (GHGs) slowed from a peak close to 0.05 W/m2 per year around 1980-85 to about 0.035 W/m2 in recent years due to slowdown of CH4 and CFC growth rates [ref. 6]. Resumed methane growth, if it continued in 2008 as in 2007, adds about 0.005 W/m2. From climate models and empirical analyses, this GHG forcing trend translates into a mean warming rate of ~0.15°C per decade.

Interestingly, a couple of major studies in the last two years have provided a forecast of significant medium-term warming. With the general caveat from the authors that the study as a whole should be viewed in a very preliminary fashion and should not be used for year-by-year predictions (and the specific caveat that the study has myriad flaws), the 2008 Nature article is consistent with the following statements:

  • The “coming decade” (2010 to 2020) is poised to be the warmest on record, globally.
  • The coming decade is poised to see faster temperature rise than any decade since the authors’ calculations began in 1960.
  • The fast warming would likely begin early in the next decade — similar to the 2007 prediction by the Hadley Center in Science.

Again, such predictions are easily influenced by La Niña and volcanoes, but barring any big surprises, NASA and Hadley are saying you can expect records to be breaking soon.

The easiest climate predictions of all:

  • The decade of the 2010s will be the hottest in the instrumental record
  • Then the decade of the 2020s will be the hottest in the instrumental record
  • Then the dec
    ade of the 2030s will be the hottest in the instrumental record
  • Then the decade of the 2040s will be the hottest in the instrumental record
  • Then the decade of the 2050s will be the hottest in the instrumental record

And, absent the strong possible GHG reductions starting immediately, that prediction can be repeated for the remaining decades of this century.

And while the temperature data before the instrumental record is obviously less reliable, the phrase “in the instrumental record” can probably already be replaced by “in the last two millenia.”

By mid-century, we’re almost certain to be “hottest in 125,000 years” (i.e. as hot as when sea levels were 15 to 20 feet higher). Final stop — an ice-free planet.

This post was created for ClimateProgress.org, a project of the Center for American Progress Action Fund.