Henry F. Diaz

Northern hemisphere surface air temperature variations: 1851–1984

Abstract A new compilation of monthly mean surface air temperature for the Northern Hemisphere for 1851–1984 is presented based on land-based meteorological station data and fixed-position weather ship data. This compilation differs from others in two ways. First, a considerable amount of new data, previously hidden away in archives, has been included, thus improving both spatial and temporal coverage. Second, the station data have been analyzed to assess their homogeneity. Only reliable or corrected station data have been used in calculating area averages. Grid point temperature estimates have been made by interpolating onto a 5° latitude by 10° longitude grid for each month of the 134 years. In the period of best data coverage, 58% of the area of the Northern Hemisphere is covered by the available data network. (The remaining area is mainly ocean too far from land-based stations to warrant extrapolation.) The reliability of hemispheric estimates is assessed for earlier periods when coverage is less than...

SPATIAL AND TEMPORAL CHARACTERISTICS OF CLIMATE IN MEDIEVAL TIMES REVISITED

Developing accurate reconstructions of past climate regimes and enhancing our understanding of the causal factors that may have contributed to their occurrence is important for a number of reasons; these include improvements in the attribution of climate change to natural and anthropogenic forcing, gaining a better appreciation for the range and magnitude of low-frequency variability and previous climatic regimes in comparison with the modern instrumental period, and developing greater insights into the relationship between human society and climatic changes. This paper examine up-to-date evidence regarding the characteristics of the climate in medieval times (A.D. 950-1400). Long and high-resolution climate proxy records reported in the scientific literature, which form the basis for the climate reconstructions, have greatly expanded in the last few decades, with greater numbers of sites that now cover more areas of the globe. Some comparisons with the modern climate record and discussion of potential mechanisms associated with the patterns of medieval climate are presented here, but our main goal is to provide the reader with some appreciation of the richness of past natural climate variability in terms of its spatial and temporal characteristics.

THE WILDFIRES OF 1910 Climatology of an Extreme Early Twentieth-Century Event and Comparison with More Recent Extremes

During the summer of 1910 large wildfires occurred throughout the western United States, and especially in the northern Rocky Mountains. The “Great Idaho Fires” of 1910 alone burned about three million acres (~1.2 Mha)— an area that is approximately the size of Connecticut. Multiple fires ignited and coalesced, burning in forests of northern Idaho and western Montana including parts of the Bitterroot, Cabinet, Clearwater, Coeur dAlene, Flathead, Kaniksu, Kootenai, Lewis and Clark, Lolo, and St. Joe National Forests. The firestorm burned for days in late August of 1910 and killed 87 people, including 78 firefighters. It is believed to be the largest, although not the deadliest, wildfire complex in recorded U.S. history. Here we show that highly anomalous weather preceded the conflagration in much of the West, including the occurrence of the warmest March on record for the contiguous United States (except March 2012). While the occurrence of very high winds greatly contributed to the fast spread of the wil...

Contributions of different time scales to extreme Paraná floods

The present study provides the first complete examination of how different time scales contributed to generate the four largest observed floods of the Paraná River (1905, 1983, 1992 and 1998). This inspection is based on the results from a previous study where an empirical method was used to decompose a 1904–2010 Paraná flow record (monthly means) into several physically meaningful oscillations with distinctive time scales or periods (few months to decades), and a secular increasing trend. We show that all the oscillations largely contributed to the four extreme floods, except an 18-year cycle that did not contribute to the 1992 flood. Sporadic intense constructive interferences between interannual-to-interdecadal (3–85 years) cycles determined (i) the favorable conditions for extreme-flood occurrence, and (ii) notable differences among floods. Indeed, in 1983, the largest flood ever recorded resulted mainly from an exceptionally strong constructive interference between cycles of 3–5, 9, 18 and 31–85 years, which are related to El Niño events, the North Atlantic Oscillation, the South Atlantic Convergence Zone, and the Pacific Ocean, respectively. Contributions of the 31–85-year cycle to the two biggest floods (1983 and 1992) are larger than the contributions of the secular upward trend, suggesting the importance of this slow oscillation in flood formation processes. The implications of our results for understanding and predicting Paraná floods are discussed.

Implications arising from models of solar irradiance: A reply to Summerhayes’ comment on ‘The Medieval Quiet Period’

Models of solar irradiance have been revised recently, leading to the current view that previous estimates of maximum total solar irradiance (TSI) in the 18th and 19th centuries were too low and should be adjusted upwards to be comparable with values in the 20th century. This adjustment is small (~0.03%) but implies a greater amplitude of irradiance change over recent centuries. This has no bearing on our concept of a Medieval Quiet Period.

Climate system studies: final report to the U.S. Department of Energy

In this final report, we summarize research on climate variability and forcing mechanisms responsible for these changes. We report on research related to high elevation climate change, changes in the hydrological cycle and the seasonality of precipitation and on changes in climatic extremes. A comprehensive bibliography of research articles and books arising from this grant is included as an appendix.