"Plants were expected to get larger with increased carbon dioxide in the atmosphere, but changes in temperature, humidity and nutrient availability seem to have _ 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 point out that warmer temperatures and changing habitats, caused by climate change, are possible reasons for the shrinking of creatures. "We do not yet know the exact mechanisms involved, or why some organisms 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 cold-blooded animals. Only two decades of warmer temperatures were enough to make reptiles  smaller. An increase of only 1degC 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. Warm-blooded 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 isn't 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 longer 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 the future. Which of the following would be the best title for the passage?
Why do some species become smaller? How does climate change in Earth's history? Climate change has many negative effects Species become smaller as climate warms