Drafting Authors: Neil Adger, Pramod Aggarwal, Shardul Agrawala, Joseph Alcamo, Abdelkader Allali, Oleg Anisimov, Nigel Arnell, Michel Boko, Osvaldo Canziani, Timothy Carter, Gino Casassa, Ulisses Confalonieri, Rex Victor Cruz, Edmundo de Alba Alcaraz, William Easterling, Christopher Field, Andreas Fischlin, Blair Fitzharris, Carlos Gay García, Clair Hanson, Hideo Harasawa, Kevin Hennessy, Saleemul Huq, Roger Jones, Lucka Kajfež Bogataj, David Karoly, Richard Klein, Zbigniew Kundzewicz, Murari Lal, Rodel Lasco, Geoff Love, Xianfu Lu, Graciela Magrín, Luis José Mata, Roger McLean, Bettina Menne, Guy Midgley, Nobuo Mimura, Monirul Qader Mirza, José Moreno, Linda Mortsch, Isabelle Niang-Diop, Robert Nicholls, Béla Nováky, Leonard Nurse, Anthony Nyong, Michael Oppenheimer, Jean Palutikof, Martin Parry, Anand Patwardhan, Patricia Romero Lankao, Cynthia Rosenzweig, Stephen Schneider, Serguei Semenov, Joel Smith, John Stone, Jean-Pascal van Ypersele, David Vaughan, Coleen Vogel, Thomas Wilbanks, Poh Poh Wong, Shaohong Wu, Gary Yohe

Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change

Evidence gleaned from the instrumental record of climate data identifies a robust, recurring pattern of ocean–atmosphere climate variability centered over the midlatitude North Pacific basin. Over the past century, the amplitude of this climate pattern has varied irregularly at interannual-to-interdecadal timescales. There is evidence of reversals in the prevailing polarity of the oscillation occurring around 1925, 1947, and 1977; the last two reversals correspond to dramatic shifts in salmon production regimes in the North Pacific Ocean. This climate pattern also affects coastal sea and continental surface air temperatures, as well as streamflow in major west coast river systems, from Alaska to California.

/pdf/a-pacific-interdecadal-climate-oscillation-with-impacts-on-4w6o1eb1un.pdf

A Pacific interdecadal climate oscillation with impacts on salmon production

The leading empirical orthogonal function of the wintertime sea-level pressure field is more strongly coupled to surface air temperature fluctuations over the Eurasian continent than the North Atlantic Oscillation (NAO). It resembles the NAO in many respects; but its primary center of action covers more of the Arctic, giving it a more zonally symmetric appearance. Coupled to strong fluctuations at the 50-hPa level on the intraseasonal, interannual, and interdecadal time scales, this "Arctic Oscillation" (AO)can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft. It is proposed that the zonally asymmetric surface air temperature and mid-tropospheric circulation anomalies observed in association with the AO may be secondary baroclinic features induced by the land-sea contrasts. The same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature, sea-level pressure, and 50-hPa height over the past 30 years: parts of Eurasia have warmed by as much as several K, sea-level pressure over parts of the Arctic has fallen by 4 hPa, and the core of the lower stratospheric polar vortex has cooled by several K. These trends can be interpreted as the development of a systematic bias in one of the atmosphere's dominant, naturally occurring modes of variability.

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/98GL00950

The Arctic oscillation signature in the wintertime geopotential height and temperature fields

A review of drought concepts

The Pacific Decadal Oscillation (PDO) has been described by some as a long-lived El Nino-like pattern of Pacific climate variability, and by others as a blend of two sometimes independent modes having distinct spatial and temporal characteristics of North Pacific sea surface temperature (SST) variability. A growing body of evidence highlights a strong tendency for PDO impacts in the Southern Hemisphere, with important surface climate anomalies over the mid-latitude South Pacific Ocean, Australia and South America. Several independent studies find evidence for just two full PDO cycles in the past century: “cool” PDO regimes prevailed from 1890–1924 and again from 1947–1976, while “warm” PDO regimes dominated from 1925–1946 and from 1977 through (at least) the mid-1990's. Interdecadal changes in Pacific climate have widespread impacts on natural systems, including water resources in the Americas and many marine fisheries in the North Pacific. Tree-ring and Pacific coral based climate reconstructions suggest that PDO variations—at a range of varying time scales—can be traced back to at least 1600, although there are important differences between different proxy reconstructions. While 20th Century PDO fluctuations were most energetic in two general periodicities—one from 15-to-25 years, and the other from 50-to-70 years—the mechanisms causing PDO variability remain unclear. To date, there is little in the way of observational evidence to support a mid-latitude coupled air-sea interaction for PDO, though there are several well-understood mechanisms that promote multi-year persistence in North Pacific upper ocean temperature anomalies.

https://link.springer.com/content/pdf/10.1023%2FA%3A1015820616384.pdf

The Pacific Decadal Oscillation

A number of recent studies have reported an ENSO-like EOF mode in the global sea surface temperature (SST) field, whose time variability is marked by an abrupt change toward a warmer tropical eastern Pacific and a colder extratropical central North Pacific in 1976‐77. The present study compares this pattern with the structure of the interannual variability associated with the ENSO cycle and documents its time history back to 1900. The analysis is primarily based on the leading EOFs of the SST anomaly and ‘‘anomaly deviation’’ fields in various domains and the associated expansion coefficient (or principal component) time series, which are used to construct global regression maps of SST, sea level pressure (SLP), and a number of related variables. The use of ‘‘anomaly deviations’’ (i.e., departures of local SST anomalies from the concurrent global-mean SST anomaly) reduces the influence of global-mean SST trends upon the structure of the EOFs and their expansion coefficient time series. An important auxiliary time series used in this study is a ‘‘Southern Oscillation index’’ based on marine surface observations. By means of several different analysis techniques, the time variability of the leading EOF of the global SST field is separated into two components: one identified with the ‘‘ENSO cycle-related’’ variability on the interannual timescale, and the other a linearly independent ‘‘residual’’ comprising all the interdecadal variability in the record. The two components exhibit rather similar spatial signatures in the global SST, SLP, and wind stress fields. The SST signature in the residual variability is less equatorially confined in the eastern Pacific and it is relatively more prominent over the extratropical North Pacific. The corresponding SLP signature is also stronger over the extratropical North Pacific, and its counterpart in the cold season 500-mb height field more closely resembles the PNA pattern. The amplitude time series of the ENSO-like pattern in the residual variability reflects the above-mentioned shift in 1976‐77, as well as a number of other prominent features, including a shift of opposite polarity during the 1940s.

/pdf/enso-like-interdecadal-variability-1900-93-1od1ppsaks.pdf

ENSO-like Interdecadal Variability: 1900–93

Monthly Mean time series of 1) surface air temperature anomalies averaged over the Northern Hemisphere based on data from land stations, 2) sea surface temperature anomalies averaged over the Northern Hemisphere oceans, and 3) 1000–500-mb thickness anomalies averaged over the region poleward of 40°N are examined The data are stratified in terms of warm (May–October) and cold (November–April) seasons Time series 1) and 3) based on cold-season data exhibit much larger month to month variability and a richer spectrum of interannual variability than those based on warm-season data: the interdecadal to century scale variability stands out more clearly in the warm-season time series Cold- and warm-season time series for 1) differ substantially, even when heavily smoothed It is hypothesized that the richer spectrum of variability in the cold-season time series is dynamically induced To test this hypothesis, departures of cold-season data for 1) and 3) from their respective smoothed warm- season tim

Interpretation of Interdecadal Trends in Northern Hemisphere Surface Air Temperature

On the basis of land station data from the Northern Hemisphere, it was determined that roughly half of the temporal variance of monthly mean hemispheric mean anomalies in surface air temperature during the period from 1900 through 1990 were linearly related to the amplitude of a distinctive spatial pattern in which the oceans are anomalously cold and the continents are anomalously warm poleward of 40 degrees north when the hemisphere is warm. Apart from an upward trend since 1975, to which El Nino has contributed, the amplitude time series associated with this pattern resembles seasonally dependent white noise. It is argued that the variability associated with this pattern is dynamically induced and is not necessarily an integral part of the fingerprint of global warming.

http://science.sciencemag.org/content/sci/270/5237/780.full.pdf

Dynamic contribution to hemispheric mean temperature trends

Indices of the dominant spatial patterns of wintertime Northern Hemisphere 500-mb height and North Pacific sea surface temperature are strongly correlated with one another on interannual and interdecadal timescales, and both am correlated with indices of the El Nin-Southern Oscillation. One possible interpretation of these relationships is that the tropical SST anomalies associated with ENSO force the atmospheric circulation over the North Pacific, and these atmospheric anomalies, in turn, give rise to the observed SST anomalies over the extratropical North Pacific. In this study, linear relationships between ENSO and extratropical variables are examined in two different ways. First, the component of the observed extratropical variability that is linearly dependent upon ENSO is removed. The dominant spatial patterns in the residual variability of 500-mb height and SST anomalies over the North Pacific are shown to be similar to their counterparts in the total fields and remain strongly coupled on ...

Yuan Zhang

Papers

A Pacific interdecadal climate oscillation with impacts on salmon production

ENSO-like Interdecadal Variability: 1900–93

Interpretation of Interdecadal Trends in Northern Hemisphere Surface Air Temperature

Dynamic contribution to hemispheric mean temperature trends

Is Climate Variability over the North Pacific a Linear Response to ENSO