This local-global connectivity is equally elusive in big cities where, because of greater interference with the environment, climatic vagaries are more frequent and pronounced. Last year, for instance, Chennai recorded its hottest day of the century. As it turned out, it was also the hottest year of the century worldwide. People immediately made the obvious—if simplistic—connection: global warming. "But, for all we know," cautions Pant, "it may well have been a local aberration. The heat-island effect, in which a thinning green canopy and thickening concrete cover dry up the earth, could have jacked up temperatures. " The onset of the heat this year too has been at a, well, scorching pace. The transition from spring to summer came 15 days too soon; Delhi got its hottest April of the decade. Weather-watchers predict another killer heat wave this summer. "With the entire northwest and central India affected, it's clearly not a case of local warming," points out S.R. Kalsi, deputy DG at Mausam Bhavan, the nodal weather monitoring authority.