"Plants were expected to get larger with increased carbon dioxide in atmosphere, but changes in temperature, humidity  and nutrient availability  seem to trumped the benefits of  increased carbon dioxide," said researchers from the National University of Singapore. 45 percent of the species studied now reach smaller adult sizes than they did in the past. The researchers pointed out that warmer temperatures and changing habitats, caused by climate change, are possible reasons for shrinking  creatures. "We do not yet know the mechanisms  involved, or why some organism are getting smaller while others are unaffected," the researchers said. "Until we understand more, we could be risking negative consequences that we can't yet quantify." The change was big in coldblooded animals. Only two decades of warmer temperatures were enough to make reptiles  smaller. An increase of 1 degree centigrade caused nearly a 10 percent increase in metabolism  . Greater use of energy resulted in tiny tortoises and little lizards. Fish are smaller now too. Though overfishing has played a part in reducing numbers, experiments show that warmer temperatures also stop fish growth. There is a recent report on warmer temperatures' negative effects on plankton , the base of the marine  ecosystem. Warmblooded animals weren't immune  from the size change caused by climate change. Many birds are now smaller. Mammals have been miniaturized too. Soay sheep are thinner. Red deer are weaker. And polar bears are smaller, compared with historical records. This is not the first time this has happened in Earth's history. 55 million years ago, a warming event similar to the current climate change caused bees, spiders and ants to shrink by 50 to 75 percent over several thousand years. That event happened over a long time than the current climate change. The speed of modern climate change could mean organisms may not respond or adapt quickly enough, especially those with long generation times. So, it is likely that more negative influences of climate change will be shown in future. Which of the following would be the best title for the passage?   _
Why do some species become smaller? Species become smaller as climate warms Climate change has many negative effects How does temperature change in Earth's history?