WASHINGTON (Reuters) - Temperatures rose sharply and suddenly in East Africa, and perhaps elsewhere, about 2,000 years ago, showing that global warming is not necessarily always caused by humans, researchers said. Aldo Shemesh of the Weizmann Institute of Science in Rehovot, Israel, and an international team of colleagues drilled into ancient sediments from a lake on the slopes of Mount Kenya. They found evidence of a four degree C (seven degree F) increase in lake water temperatures between 350 BC and 450 AD. "Our findings show that the climate can warm up suddenly without any connection to human activity," Shemesh said in a statement. Writing in the journal Science, the scientists said the warming of the lake water almost certainly reflected an overall warming trend in East Africa at the time. They noted that other researchers had found evidence of similar warming at about the same time in Sweden and Alaska, so the warming trend may have been global. "Documenting climatic changes that took place in the past in various parts of the globe may help scientists make more precise predictions about the potential effects of modern activity on the climate of the future," Shemesh said. Most scientists agree that the global climate has warmed about half a degree C (one degree F) over the past century. Last month was the hottest month around the world, on average, ever recorded - although records only go back a few hundred years and are spotty. There are still disagreement over whether humanity is responsible for all or part of global warming, which may be responsible for weather disruptions such as storms and droughts.