Relative impacts of human-induced climate change and natural climate variability

Abstract

Spectral analysis of the sub-tropical percentage data (Fig. 4) indicates coherence with the 23±19-kyr oscillations (precession) just below the 80% con®dence interval. The effects of the seasonality and precipitation produced by the increased amplitude of the seasonal cycle of solar radiation appear to have had a signi®cant in¯uence on the distribution and composition of the sub-tropical vegetation in the Hungarian late Pliocene.The pollen spectrum of both taxonomic groups (that is, boreal and sub-tropical) is, however, dominated by a strong low-frequency component of ,124 kyr. Even though there are only at most three cycles to be resolved in this data set, such variance is clearly visible in the record (Fig. 3). This is of particular signi®cance, as the 124-kyr peak is non-existent in the calculated insolation forcing (Fig. 4) 15 .There is some evidence from oceanic records of signi®cant environmental change at the 95±124-kyr interval. Dust data in deep sea cores exhibit a strong response at this period in the time interval considered here 20 . Changes in atmospheric dust content are thought to re¯ect directly changes in continental aridity and terrestrial vegetation cover 21 , but until now there has been little direct pollen evidence to support this suggestion. The 124-kyr variance observed in our pollen record strongly supports the link between the dust content observed in marine cores and terrestrial vegetation change.The results from Pula thus indicate that in addition to forcing at the orbital frequencies of precession and obliquity, internally driven nonlinear responses of the climate system at a period of ,124 kyr were as important (if not more important) in driving terrestrial vegetation dynamics and were presumably associated with this broad-scale environmental change. This terrestrial sequence provides the basis for beginning to understand the physical relationships between vegetation, ice volume and insolation forcing during a critical period in the Earth's climate system. M

Tropical drying trends in global warming models and observations

“…6 over their periods of availability, since 1979 and since about 1950, respectively, with a Spearman-rho test applied at each grid point. The coarserresolution Hulme land rainfall data (20) give similar results (data not shown). The station-based local negative trends fall in the range of 5-30% of the mean rainfall per 100 yr; the shorter satellite-based trend is somewhat larger.…”

Jetstream and rainfall distribution in the Mediterranean region

“…The rainfall distribution in the Mediterranean region is important, because this region is at risk of water shortage (Hulme et al, 1999). In fact, an elaboration of the data reported by Marshall et al (2001a) and by Hurrell (1995) shows that from December to March it rains 30 % more in North Europe than in South Europe.…”

Quantifying uncertainty in urban flooding analysis considering hydro-climatic projection and urban development effects

“…They show that one catchment is highly dominated by natural variability, while the other catchment is strongly affected by climate change. Hulme et al (1999) explain that if a region is more dominated by natural variability than by climate change, adaptation management that takes into account natural variability may be sufficient to withstand climate change. Our results show that future flood management in the Fanno and Johnson creek catchments should consider climate change impact as well as historical natural climate variability.…”