NOAA. The data analysis system used by NOAA for global temperature analyses over the past eight years indicates that 2005 would likely be the second-warmest year on record (1.06º F; 0.59º C above the 1880-2004 mean), marginally lower than 1998. (NOAA is in the process of transitioning to an improved global temperature analysis system.)

NOAA found that the largest temperature anomalies were widespread throughout high latitude regions of the Northern Hemisphere and included much of Russia, Scandinavia, Canada and Alaska. During the past century, global surface temperatures have increased at a rate near 1.1º F/Century (0.6º C/Century), but the rate of temperature increase has been three times larger since 1976, with some of the largest temperature increases occurring in the high latitudes.

NOAA attributes the very small differences (on the order of a few hundredths of a degree Celsius) between the NOAA data sets as well as those developed by other organizations, such as NASA and the United Kingdom Meteorological Office (Hadley Centre) to differing methodologies that must address areas of the globe with sparse observations and/or measurement biases.

According to the agency, the uncertainties associated with these factors and methodologies make 2005 statistically indistinguishable from 1998 as well as other recent years such as 2002 and 2003 in all data sets.

NOAA’s chart of global significant climate anomalies and events in 2005. Click to enlarge.

NASA Goddard Institute for Space Studies (GISS). GISS determined that 2005 showed the highest average global surface temperature in more than a century of instrumental data—an increase of 0.6º C over the mean. The error bar on the data implies that 2005 is practically in a dead heat with 1998, the warmest previous year.

GISS. (Top) Global annual surface temperature relative to 1951-1980 mean based on surface air measurements. (Bottom) Temperature anomaly for 2005 meteorological year (December 2004 through November 2005). Click to enlarge.

The GISS analysis used documented procedures for data over land, satellite measurements of sea surface temperature since 1982, and a ship-based analysis for earlier years. The estimated error in comparing nearby years, such as 1998 and 2005, increases from 0.05°C in recent years to 0.1°C at the beginning of the 20th century.

GISS also characterized the record warmth in 2005 as notable due to the lack of a boost from a tropical El Niño this year. The 1998 meteorological year, on the contrary, was lifted 0.2°C above the trend line by the strongest El Niño of the past century.

Global warming is now 0.6°C in the past three decades and 0.8°C in the past century. It is no longer correct to say that “most global warming occurred before 1940.” More accurately, there was slow global warming, with large fluctuations, over the century up to 1975 and subsequent rapid warming of almost 0.2°C per decade.

Goddard’s map of current warmth again shows the largest results at the high latitudes in the Northern Hemisphere. The remote location of most warming makes it clear, according to the GISS analysis, that the warming is not a product of local urban influence.

World Meteorological Organization (WMO). WMO found that the global mean surface temperature in 2005 is currently estimated to be 0.48º C above the 1961-1990 annual average (14ºC), according to the records maintained by Members of the World Meteorological Organization (WMO).

That makes 2005 is currently the second-warmest year on record and likely to be among the warmest 4 years in the temperature record since 1861; WMO, however, will not release official figures until February.

By WMO’s analysis, 1998 remains the warmest year, with optimum averaged surface temperatures averaging 0.54ºC above the same 30-year mean. The uncertainty in the global temperature values, arising mainly from gaps in data coverage, are such that 2005 could be the warmest year or the eighth warmest year on record, according to WMO which also concurs that the last 10 years (1996-2005) are the warmest years on record.

WMO’s global temperature analyses are based on three different datasets. These include the annual optimally averaged global and hemispheric data series, maintained by the Hadley Centre of the Met Office, UK, from which the official rankings are sourced. The other two data sets are the combined dataset maintained by the Hadley Centre of the Met Office, UK, and the Climatic Research Unit, University of East Anglia, UK, from which the latest values are derived, and a dataset maintained by the USA Department of Commerce's National Oceanic and Atmospheric Administration (NOAA). Results from these two datasets are comparable.

Hadley. Annual combined land surface air temperature and SST anomalies, 1861-2005, with respect to the 1961-1990 mean. Click to enlarge.

Hadley Centre of the Met Office and the University of East Anglia (UEA), UK. Provisional data from the Hadley Centre and the UEA suggests that average sea and land temperature is currently 0.65ºC above the long-term average. The UK has experienced a particularly warm year, with the central England temperature (CET) 1.07ºC above normal.

The southern hemisphere appears to be experiencing its fourth warmest year ever, with average sea and land temperature around 0.32ºC above average.

These figures show that global warming is continuing and are consistent with what we expect to occur from our research into greenhouse gas emissions

—Adam Scaife, Hadley Center

The assessment from NASA Goddard is a bit more pointed with respect to the greenhouse gas issue:

Recent warming coincides with rapid growth of human-made greenhouse gases. Climate models show that the rate of warming is consistent with expectations. The observed rapid warming thus gives urgency to discussions about how to slow greenhouse gas emissions.

Contributing to the consternation over ongoing global warming will be research to be published in the current issue of Nature by scientists from the Hadley Centre that indicates that the cooling effect of man-made aerosols (i.e., air pollution) may be having a greater direct effect on our climate than previously thought.

Small airborne particles—aerosols—have a direct cooling effect on the Earth’s climate through the scattering and absorption of the sun’s incoming radiation. It is known that this cooling effect has offset 20th century global warming to some degree and without this, temperatures would have risen at a faster rate.

Using extensive observations from aircraft, ground- and satellite-based instruments, the study has shown that the direct effect of man-made aerosols on the climate may be greater than previous estimates.

The findings are the first to separate man-made and natural aerosols on a global scale using observations.

Being able to separate the contribution from natural aerosols using observations is needed in order to estimate the cooling effect of man-made aerosols. We can show that these estimates are less uncertain than those from computer models.

If computer models are indeed underestimating the strength of the cooling by man-made aerosols, they may also underestimate climate warming. Of course, a reduction in aerosols will lead to an increase in global warming but is necessary to counter local pollution.

—Nicolas Bellouin, study leader

Resources:

• Real Climate Discussion on 2005 temperatures

• Real Climate Discussion on “random walk“ warming