2011 was the warmest year on record during which a La Niña occurred. World temperatures are generally lower in La Niña years than non-La Niña years.
1998 was also an especially warm year, in fact, the warmest year in the 20th century. 1998 was an El Niño year, in fact, the most extreme El Niño recorded to date. World temperatures are generally higher in El Niño years.
La Niña and El Niño are part of a climate system called the El Niño/southern oscillation which has profound effects on the world’s weather and which scientists have been studying for some time. Depending upon if and how it is operating at a given time, the system can raise or depress temperatures in a given year.
The El Niño/southern oscillation (ENSO) is one of those systems often referenced by climate change deniers as producing “natural variations” in climate. What is often left out by climate disinformers is the fact that climatologists are well-aware of these periodic and returning systems. Another well-known one is the eleven-year solar cycle, and in accounting for climate, volcanic aerosols are also an important factor. All of these represent “noise” in the climate record, noise which must be accounted for and removed from the climate record in order to measure any underlying trends unaccounted for by systems like these.
I wrote about a study made on this subject before. (See Removing noise from the climate record: a case study.) Now two other scientists have approached the problem again, and have completed a new study updated to 2010. In this study they removed the affects of ENSO, volcanic aerosols and solar variation to produce a graph of underlying climate change. The graph analyzes the following datasets.
GISS = NASA
NCDC = National ClimaticDataCenter
CRU = Hadley Centre/Climatic Research Unit
RSS = Remote Sensing Systems – satellite record
UAH =University of Alabama in Huntsville–satellite record
Here is the graph.
As you can see by this graph, the dataset that underplays the climate signal the most is the one from HadleyCentre/Climatic Research Unit. This dataset (a favourite of climate change deniers) is known to underplay warming in the Arctic, where in fact warming is taking place the fastest. Nonetheless, all the corrected datasets show a steady rise in temperature between 1980 and 2010.
Here is a graph showing the average of the five datasets.
As you can see the temperature rise is steady. It hasn’t slowed or stopped. With the exception of 1998, every year in the 21st century has been higher than every year in the 20th century, and every year since 2005 has been warmer than 1998.
Here’s the study this information is taken from together with its abstract.
Grant Foster and Stefan Rahmstorf, “Global temperature evolution 1979-2010” (2011) Environ. Res. Lett. 6 044022 doi:10.1088/1748-9326/6/4/044022
We analyze five prominent time series of global temperature (over land and ocean) for their common time interval since 1979: three surface temperature records (from NASA/GISS, NOAA/NCDC and HadCRU) and two lower-troposphere (LT) temperature records based on satellite microwave sensors (from RSS and UAH). All five series show consistent global warming trends ranging from 0.014 to 0.018 K yr−1. When the data are adjusted to remove the estimated impact of known factors on short-term temperature variations (El Niño/southern oscillation, volcanic aerosols and solar variability), the global warming signal becomes even more evident as noise is reduced. Lower-troposphere temperature responds more strongly to El Niño/southern oscillation and to volcanic forcing than surface temperature data. The adjusted data show warming at very similar rates to the unadjusted data, with smaller probable errors, and the warming rate is steady over the whole time interval. In all adjusted series, the two hottest years are 2009 and 2010.