1 AUGUST 2011
MANABE ET AL.
3817
Seasonal Variation of Surface Temperature Change during the Last Several Decades SYUKURO MANABE Program in Atmospheric and Oceanic Sciences, Princeton University, Princeton, New Jersey
JEFFREY PLOSHAY AND NGAR-CHEUNG LAU NOAA/Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey (Manuscript received 7 March 2011, in final form 18 May 2011) ABSTRACT Using the historical surface temperature dataset compiled by Climatic Research Unit of the University of East Anglia and the Hadley Centre of the United Kingdom, this study examines the seasonal and latitudinal profile of the surface temperature change observed during the last several decades. It reveals that the recent change in zonal-mean surface air temperature is positive at practically all latitudes. In the Northern Hemisphere, the warming increases with increasing latitude and is large in the Arctic Ocean during much of the year except in summer, when it is small. At the Antarctic coast and in the northern part of the circumpolar ocean (near 558S), where limited data are available, the changes appear to be small during most seasons, though the warming is notable at the coast in winter. However, this warming is much less than the warming over the Arctic Ocean. The seasonal variation of the surface temperature change appears to be broadly consistent with the result from a global warming experiment that was conducted some time ago using a coupled atmosphere–ocean–land model.
1. Introduction Seasonal variation in the latitudinal profile of global warming has been the subject of many modeling studies (e.g., Manabe and Stouffer 1979, 1980; Robock 1983; Manabe et al. 1992). For example, Manabe et al. (1992) analyzed the seasonal response of a coupled atmosphere– ocean–land model to gradually increasing concentration of atmospheric carbon dioxide. Figure 1 illustrates the latitude–calendar month distribution of zonal-mean surface air temperature response averaged over the 61st to the 80th years of the experiment, when CO2 concentration of air doubles. It shows that surface temperature increases at all latitudes throughout the year. In the Northern Hemisphere, the warming increases with increasing latitude and is large over the Arctic Ocean during much of the year except in summer, when it is at a minimum. In contrast, in the Southern Hemisphere, the warming is small in the circumpolar ocean (508–708S), in
Corresponding author address: Dr. Syukuro Manabe, Program in Atmospheric and Oceanic Sciences, Princeton University, Sayre Hall, 300 Forrestal Road, Princeton, NJ 08540. E-mail:
[email protected] DOI: 10.1175/JCLI-D-11-00129.1 Ó 2011 American Meteorological Society
qualitative agreement with more recent model projections, summarized by Meehl et al. (2007). The large seasonal variation of warming over the Arctic Ocean of the coupled model is attributable to the reduction in sea ice thickness, as discussed by Manabe and Stouffer (1979, 1980). During the cold season, when seawater temperature beneath sea ice is much warmer than surface air temperature above sea ice, the upward heat conduction through the sea ice layer is inversely proportional to the thickness of that layer. When the thickness of sea ice decreases due to global warming, it is therefore expected that the rate of upward heat conduction through sea ice increases, yielding large surface warming in winter. In summer and early fall, when the area coverage of sea ice is at a minimum and the absorption of solar radiation is at a maximum, surface temperature remains near the freezing point of seawater due to the melting of sea ice. This explains why surface temperature hardly increases over the Arctic Ocean in summer. In the circumpolar ocean of the Southern Hemisphere, the warming is small mainly because of the deep vertical mixing of heat, as discussed by Stouffer et al. (1989) and Manabe et al. (1991). Chapman and Walsh (1993) examined the overall seasonal behavior of Arctic land station temperatures
3818
JOURNAL OF CLIMATE
FIG. 1. Latitude–calendar month distribution of the change in zonal-mean surface air temperature of a coupled atmosphere–ocean– land model in response to the doubling of the CO2 concentration of air (Manabe et al. 1992). The change is the difference between the 100-yr mean state of the control experiment and the 20-yr mean state from the 61st to the 80th year of the global warming experiment, when the CO2 concentration doubles. Here, surface air temperature represents the temperature at the lowest finite difference level of the model located ;70 m above the earth’s surface. Units are in 8C.
between 1961 and 1990. Their results show that in winter and spring, warming dominated with values of about 0.25 and 0.58C decade21, respectively. In summer the trend was near zero, and in autumn the trend was either neutral or showed a slight cooling. Their result appears to be broadly consistent with the seasonal variation of the surface warming presented in Fig. 1. Using the latest global atmospheric reanalysis dataset produced by the European Centre for Medium-Range Weather Forecasts [ECMWF; the ECMWF Interim reanalysis (ERA-Interim); see Berrisford et al. 2009; Dee and Uppala 2009], Screen and Simmonds (2010) analyzed the seasonal variation of the atmospheric temperature trend in high northern latitudes during the last two decades (i.e., 1989–2008). They found that over the Arctic Ocean, the warming trend is pronounced near the earth’s surface in most seasons of the year, though the nearsurface warming is more modest in summer. They suggested that the large seasonal dependence of the warming is attributable in no small part to the reduction of sea ice thickness. The accelerated reduction of sea ice during the last few decades has been the subject of many recent studies (e.g., Rigor and Wallace 2004). This study evaluates how the latitudinal profile of the surface temperature trend varies seasonally, using the
VOLUME 24
FIG. 2. Zonal-mean surface temperature anomaly averaged over the period from 1991 to 2009. Here, the anomaly represents the deviation from the zonal mean averaged over the 30-yr base period from 1961 to 1990. Because of the poor data coverage, the anomaly is not shown poleward of 808N and 608S (see Fig. 4 for the seasonal variation of the anomalies at the Antarctic coast). Units are in 8C. To facilitate the comparison of this figure with Fig. 1, color areas are chosen such that the contour values at color thresholds are 1/ 5th of those in Fig. 1. The selection is made because the anomaly in Fig. 2 is approximately 1/ 5th of the change in Fig. 1.
historical surface temperature dataset compiled by the Climatic Research Unit of the University of East Anglia and the Hadley Centre of the United Kingdom. The analysis was made for both the Northern and Southern Hemispheres, covering the period over the last several decades (i.e., 1961–2009). The result of the analysis is compared with the model-projected change in surface temperature due to CO2 doubling, presented in Fig. 1.
2. Data We use the improved version of historical surface temperature dataset HadCRUT3 (Brohan et al. 2006), which is a collaborative product of the Met Office Hadley Centre and the Climatic Research Unit at the University of East Anglia. The dataset provides, on a 58 grid, information on the geographical distribution of the yearly and monthly surface temperature anomaly, defined as the deviation from the average over the 30-yr base period between 1961 and 1990. The anomaly is averaged over the 19-yr period between 1991 and 2009, so that the influence of interannual variability is removed. To capture the interdecadal trend of the seasonal variation
1 AUGUST 2011
MANABE ET AL.
3819
FIG. 3. Geographical distributions of surface air temperature anomaly obtained for the two 3-month periods of (a) DJF and (b) JJA averaged over the 19-yr period from 1991 to 2009. Here, the anomaly represents the deviation from the temperature averaged over the 30-yr base period from 1961 to 1990. Units are in 8C.
of surface temperature, we used the data from only those grid points, where the anomaly is available for every month of a year in at least 15 yr out of the 19-yr period between 1991 and 2009. The anomaly is the change in surface temperature from the base period of 1961–90 to the recent 19-yr period of 1991–2009. Because these two periods are centered around 1975 and 2000, which are 25 yr apart, one can estimate the surface temperature trend per decade, dividing the anomaly of the recent period by 2.5. The change may also be regarded as an indicator of the trend in surface temperature over the last half century [for the analysis of surface temperature trends over shorter time segments, see the study conducted by Jones et al. (1999)].
3. Results Figure 2 illustrates the latitude–calendar month profile of the zonal-mean anomaly of the surface air temperature averaged over the 19-yr period from 1991 to 2009. It shows that the anomaly of surface temperature is positive at practically all latitudes. In the Northern Hemisphere, the temperature anomaly increases with increasing latitude and is large during much of the year with the exception of summer, when it is at a minimum over the Arctic Ocean. In the Southern Hemisphere, the anomaly is small around 558S during most of the year. The seasonal and latitudinal profile of the observed warming described above appears to be broadly consistent with that of the warming obtained from the coupled
3820
JOURNAL OF CLIMATE
VOLUME 24
FIG. 4. (bottom) Monthly variation of 3-month running-mean surface air temperature anomalies at the 14 grid points located along the coast of the Antarctic continent between 62.58 and 77.58S. The monthly variation of the average anomaly (i.e., the arithmetic average over all grid points) is shown at the right-hand side. (top) Bar diagram of annual-mean anomalies at all of the grid points. The arithmetic average of the annual-mean anomalies is listed at the upper right. Units are in 8C.
model (Fig. 1), though there is notable difference in details. Figures 3a and 3b illustrate the geographical distributions of the anomalies averaged over the 3-month periods of December–February (DJF) and June–August (JJA), respectively. In general, the anomaly is positive almost everywhere, though there are small light blue patches with small negative anomalies. A notable exception is the narrow belt of relatively large negative winter (DJF) anomaly along the east coast of the North American continent. In general, the anomaly is larger over continents than over oceans and is particularly pronounced over the Eurasian and North American continents in winter. At the Antarctic coast and in the northern part of the circumpolar ocean between 50 and 608S, most of the anomalies are weakly negative in Southern Hemisphere summer (DJF). In contrast, positive Southern Hemisphere winter (JJA) anomalies are indicated at the Antarctic coast and near the Cape Horn of South America. The positive winter (JJA) anomaly is particularly large at a grid box that includes Vernadsky station (65.28S, 64.38W), located on the west coast of the
Antarctic Peninsula. An exception is also seen at the grid point that includes U.K. Halley station (75.58S, 26.68W), where the winter (JJA) anomaly has a relatively large negative value. In general, however, the large-scale patterns shown in Figs. 3a and 3b resemble the patterns of the model-projected surface air temperature change due to gradual CO2 doubling, as obtained by Manabe et al. (1992, their Figs. 9a and 9b). Because of sparse data coverage, the seasonal variation of the zonal-mean anomaly is not shown poleward of 608S. For the sake of completeness, we inspect the seasonal variations of the anomalies at the 14 grid points located along the Antarctic coast [see also the study of Turner et al. (2005), for the trend analysis of surface temperature at the stations located along the Antarctic coast]. The bottom panel of Fig. 4 illustrates the monthly variation of 3-month running-mean surface air temperature anomalies at the grid points located between 62.58 and 77.78S. The panel shows that the seasonal variation of the anomaly is particularly pronounced at the two grid boxes that contain the Vernadsky and Halley stations mentioned above. At Vernadsky station, the anomaly is
1 AUGUST 2011
3821
MANABE ET AL.
positive throughout the year and is very large in winter and early spring. At the Halley station, the anomaly is negative throughout the year, with the largest negative value in the fall. At a majority of the other grid points near the Antarctic coast, however, the anomalies are smaller, though they tend to have positive and negative values during the cold and warm halves of the year, respectively. When averaged over all grid points, the anomaly has a positive value in winter and early spring and has a small value during the rest of a year, as shown in the right panel of Fig. 4. In general, the winter anomalies at the Antarctic coast are much smaller than those in the Arctic, with the notable exception of the west coast of the Antarctic Peninsula. Averaging the annual-mean anomalies shown in the top panel, one gets 0.158C, as indicated at the right end of the top panel. This is much smaller than the annual-mean anomaly over the Arctic Ocean.
4. Conclusions According to the analysis presented here, the trend in zonal-mean surface air temperature is positive during the last several decades at practically all latitudes. In the Northern Hemisphere, the warming increases with increasing latitude and is large in the Arctic Ocean during much of the year except in summer and early fall, when it is small. At the Antarctic coast and in the northern part of the circumpolar ocean between 508 and 608S, where limited data are available, the change appears to be small during most of the year, though the warming trend is notable at the coast in winter. It is, however, much less than the warming over the Arctic Ocean. The seasonal variation of the surface temperature trend described above appears to be broadly consistent with the profile obtained from a global warming experiment that was conducted two decades ago using a coupled atmosphere– ocean–land model. Acknowledgments. We are grateful to Drs. P. J. Brohan, J. Kennedy, I. Harris, S. F. B. Tett, and P. D. Jones, who constructed the historical surface temperature dataset ‘‘HadCRUT3’’ and made it freely available, thereby enabling us to conduct the analysis presented here. We appreciate the contribution of Aditya Salgame during the initial phase of this study. This report was prepared under Award NA080AR4320752 from the National Oceanic and Atmospheric Administration, U.S. Department of Commerce. The statements, findings, conclusions, and
recommendations are those of the authors and do not necessarily reflect the views of the National Oceanic and Atmospheric Administration, or the U.S. Department of Commerce. REFERENCES Berrisford, P., D. P. Dee, K. Fielding, M. Fuentes, P. Ka˚llberg, S. Kobayashi, and S. M. Uppala, 2009: The ERA-Interim archive, version 1.0. ECMWF ERA Rep. Series 1, 20 pp. [Available online at http://www.ecmwf.int/publications/library/do/references/ list/782009.] Brohan, P., J. J. Kennedy, I. Harris, S. F. B. Tett, and P. D. Jones, 2006: Uncertainty estimate in regional and global observed temperature changes: A new data set from 1850. J. Geophys. Res., 111, D12106, doi:10.1029/2005JD006548. Chapman, W. L., and J. E. Walsh, 1993: Recent variation of sea ice and air temperature in high latitudes. Bull. Amer. Meteor. Soc., 74, 33–47. Dee, D. P., and S. Uppala, 2009: Variational bias correction of satellite radiance data in the ERA-Interim reanalysis. Quart. J. Roy. Meteor. Soc., 135, 1830–1841. Jones, P. D., M. New, D. E. Parker, S. Martin, and I. G. Rigor, 1999: Surface air temperature and its variation over the last 150 years. Rev. Geophys., 37, 173–199. Manabe, S., and R. J. Stouffer, 1979: A CO2-climate sensitivity study with a mathematical model of the global climate. Nature, 282, 491–493. ——, and ——, 1980: Sensitivity of a global climate model to an increase of CO2 concentration in the atmosphere. J. Geophys. Res., 85, 5529–5554. ——, ——, M. J. Spelman, and K. Bryan, 1991: Transient response of a coupled ocean–atmosphere model to gradual changes of atmospheric CO2. Part I: Annual mean response. J. Climate, 4, 785–818. ——, M. J. Spelman, and R. J. Stouffer, 1992: Transient response of a coupled ocean–atmosphere model to gradual changes of atmospheric CO2. Part II: Seasonal response. J. Climate, 5, 105–126. Meehl, G. A., and Coauthors, 2007: Global climate projections. Climate Change 2007: The Physical Science Basis, S. Solomon et al., Eds., Cambridge University Press, 747–845. Rigor, I. G., and J. M. Wallace, 2004: Variation in the age of Arctic sea-ice and summer sea-ice extent. Geophys. Res. Lett., 31, L09401, doi:10.1029/2004GL019492. Robock, A., 1983: Ice and snow feedbacks and latitudinal and seasonal distribution of climate sensitivity. J. Atmos. Sci., 40, 986–997. Screen, J. A., and I. Simmonds, 2010: The central role of diminishing sea ice in recent Arctic temperature amplification. Nature, 464, 1334–1337, doi:10.1038/nature09051. Stouffer, R. J., S. Manabe, and K. Bryan, 1989: Interhemispheric asymmetry in climate response to a gradual increase of atmospheric CO2. Nature, 342, 660–662. Turner, J., and Coauthors, 2005: Antarctic climate change during the last 50 years. Int. J. Climatol., 25, 279–294, doi:10.1002/joc.1130.
