Since 65 million years ago (Ma), Earth's climate has undergone a significant and complex evolution, the finer details of which are now coming to light through investigations of deep-sea sediment cores. This evolution includes gradual trends of warming and cooling driven by tectonic processes on time scales of 10(5) to 10(7) years, rhythmic or periodic cycles driven by orbital processes with 10(4)- to 10(6)-year cyclicity, and rare rapid aberrant shifts and extreme climate transients with durations of 10(3) to 10(5) years. Here, recent progress in defining the evolution of global climate over the Cenozoic Era is reviewed. We focus primarily on the periodic and anomalous components of variability over the early portion of this era, as constrained by the latest generation of deep-sea isotope records. We also consider how this improved perspective has led to the recognition of previously unforeseen mechanisms for altering climate.

Dyadic data matrices, such as co-occurrence matrix, rating matrix, and proximity matrix, arise frequently in various important applications. A fundamental problem in dyadic data analysis is to find the hidden block structure of the data matrix. In this paper, we present a new coclustering framework, block value decomposition(BVD), for dyadic data, which factorizes the dyadic data matrix into three components, the row-coefficient matrix R, the block value matrix B, and the column-coefficient matrix C. Under this framework, we focus on a special yet very popular case -non-negative dyadic data, and propose a specific novel co-clustering algorithm that iteratively computes the three decomposition matrices based on the multiplicative updating rules. Extensive experimental evaluations also demonstrate the effectiveness and potential of this framework as well as the specific algorithms for co-clustering, and in particular, for discovering the hidden block structure in the dyadic data.

The relation between the partial pressure of atmospheric carbon dioxide (pCO2) and Paleogene climate is poorly resolved. We used stable carbon isotopic values of di-unsaturated alkenones extracted from deep sea cores to reconstruct pCO2 from the middle Eocene to the late Oligocene (approximately 45 to 25 million years ago). Our results demonstrate that pCO2 ranged between 1000 to 1500 parts per million by volume in the middle to late Eocene, then decreased in several steps during the Oligocene, and reached modern levels by the latest Oligocene. The fall in pCO2 likely allowed for a critical expansion of ice sheets on Antarctica and promoted conditions that forced the onset of terrestrial C4 photosynthesis.

Global Cooling During the Eocene-Oligocene www.sciencemag.org (this information is current as of February 27, 2009 ):The following resources related to this article are available online at

& the Expedition 302 Scientists †The Palaeocene/Eocene thermal maximum, ,55 million years ago, was a brief period of widespread, extreme climatic warming [1][2][3] , that was associated with massive atmospheric greenhouse gas input 4 . Although aspects of the resulting environmental changes are well documented at low latitudes, no data were available to quantify simultaneous changes in the Arctic region. Here we identify the Palaeocene/Eocene thermal maximum in a marine sedimentary sequence obtained during the Arctic Coring Expedition 5 . We show that sea surface temperatures near the North Pole increased from ,18 8C to over 23 8C during this event. Such warm values imply the absence of ice and thus exclude the influence of ice-albedo feedbacks on this Arctic warming. At the same time, sea level rose while anoxic and euxinic conditions developed in the ocean's bottom waters and photic zone, respectively. Increasing temperature and sea level match expectations based on palaeoclimate model simulations 6 , but the absolute polar temperatures that we derive before, during and after the event are more than 10 8C warmer than those model-predicted. This suggests that higher-than-modern greenhouse gas concentrations must have operated in conjunction with other feedback mechanisms-perhaps polar stratospheric clouds 7 or hurricane-induced ocean mixing 8 -to amplify early Palaeogene polar temperatures.

Climate sensitivity-the mean global temperature response to a doubling of atmospheric CO 2 concentrations through radiative forcing and associated feedbacks-is estimated at 1.5-4.5• C (ref. 1). However, this value incorporates only relatively rapid feedbacks such as changes in atmospheric water vapour concentrations, and the distributions of sea ice, clouds and aerosols 2 . Earth-system climate sensitivity, by contrast, additionally includes the effects of long-term feedbacks such as changes in continental ice-sheet extent, terrestrial ecosystems and the production of greenhouse gases other than CO 2 . Here we reconstruct atmospheric carbon dioxide concentrations for the early and middle Pliocene, when temperatures were about 3-4• C warmer than preindustrial values [3][4][5] , to estimate Earth-system climate sensitivity from a fully equilibrated state of the planet. We demonstrate that only a relatively small rise in atmospheric CO 2 levels was associated with substantial global warming about 4.5 million years ago, and that CO 2 levels at peak temperatures were between about 365 and 415 ppm. We conclude that the Earth-system climate sensitivity has been significantly higher over the past five million years than estimated from fast feedbacks alone.The magnitude of Earth-system climate sensitivity can be assessed by evaluating warm time intervals in Earth history, such as the peak warming of the early Pliocene ∼4-5 million years ago (Myr). Mean annual temperatures during the middle Pliocene (∼3.0-3.3 Myr) and early Pliocene (4.0-4.2 Myr) were ∼2.5• C (refs 3, 4), and 4• C (ref. 5) warmer than preindustrial conditions, respectively. During the early Pliocene, the equatorial Pacific Ocean maintained an east-west sea surface temperature (SST) gradient of only ∼1.5• C, which arguably resembles permanent El Niño-like conditions 6 . Meridional 5,7 and vertical ocean temperature gradients 8 were reduced, and deep-ocean ventilation enhanced, relative to today 9,10 . Deterioration in Earth's climate state from 3.5 to 2.5 Myr led to an increase in Northern Hemisphere glaciation 11 . By ∼2 Myr, subtropical Pacific meridional SST gradients resembled modern conditions 5 , and the Pacific zonal SST gradient (∼5• C) was similar to the gradient observed today, with a strong Walker circulation 6 . Tectonics and changes in ocean [12][13][14] and atmospheric circulation 15,16 were potentially important factors in climate evolution during this time. However, an assessment of the timing of oceanographic and climate changes 17 , and the stability of the Greenland ice sheet to a range of possible forcings 18 , implicate atmospheric CO 2 as the primary factor driving the warmth of the early Pliocene and the onset of Northern Hemisphere glaciation.For this study, we evaluate the magnitude of CO 2 change and Earth-system climate sensitivity during the Pliocene by using the alkenone-CO 2 method to reconstruct Pleistocene-Pliocene pCO 2 histories from six ocean localities. Ocean sites used in this study Alkenones are long-chained (C 37 -C ...

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The Palaeocene/Eocene thermal maximum represents a period of rapid, extreme global warming 55 million years ago, superimposed on an already warm world. This warming is associated with a severe shoaling of the ocean calcite compensation depth and a >2.5 per mil negative carbon isotope excursion in marine and soil carbonates. Together these observations indicate a massive release of 13C-depleted carbon and greenhouse-gas-induced warming. Recently, sediments were recovered from the central Arctic Ocean, providing the first opportunity to evaluate the environmental response at the North Pole at this time. Here we present stable hydrogen and carbon isotope measurements of terrestrial-plant- and aquatic-derived n-alkanes that record changes in hydrology, including surface water salinity and precipitation, and the global carbon cycle. Hydrogen isotope records are interpreted as documenting decreased rainout during moisture transport from lower latitudes and increased moisture delivery to the Arctic at the onset of the Palaeocene/Eocene thermal maximum, consistent with predictions of poleward storm track migrations during global warming. The terrestrial-plant carbon isotope excursion (about -4.5 to -6 per mil) is substantially larger than those of marine carbonates. Previously, this offset was explained by the physiological response of plants to increases in surface humidity. But this mechanism is not an effective explanation in this wet Arctic setting, leading us to hypothesize that the true magnitude of the excursion--and associated carbon input--was greater than originally surmised. Greater carbon release and strong hydrological cycle feedbacks may help explain the maintenance of this unprecedented warmth.