The Earth is warming. Here are the top warning signs, according to experts

The amount of greenhouse gases being emitted into Earth's atmosphere has reached such a high level that it will take major changes around the world to mitigate the effects on climate change, experts say. Greenhouse gasses such as carbon dioxide, which trap the sun's heat, are the "most significant driver of observed climate change since the mid-20th century," according to the U.S. Environmental Protection Agency. To illustrate the pace of change, the National Oceanographic and Atmospheric Administration's greenhouse gas index, which measures the impact of the gasses on climate, indicates it took approximately 240 years to go from 0 to 1, based on a 1990 benchmark. In the less than three decades since, the index says it has risen another 43% above the baseline. "Climate change is now affecting every country on every continent. It is disrupting national economies and affecting lives, costing people, communities and countries dearly today and even more tomorrow," the UN says on its sustainable development site. "Weather patterns are changing, sea levels are rising, weather events are becoming more extreme and greenhouse gas emissions are now at their highest levels in history." Here are the top issues contributing to climate change, according to the experts: Contributing factors Extraction of fossil fuels The extraction of fossil fuels is one of the top issues affecting climate change, said Elizabeth Yeampierre, founder and executive director of UPROSE, a New York-based organization that promotes sustainability, and co-chair of the Climate Justice Alliance, a network supporting the climate justice movement. "We're literally going deeper and taking out fossil fuel when the science is telling us that we have to stop," Yeampierre said. Fossils fuels can't continue to be burned at the current rate "if we want to have a stable climate," said Lindsey Allen, executive director of the nonprofit Rainforest Action Network. "We immediately need to stop expanding our extraction of coal, and oil and gas," she said. Burning fossil fuels emits large amounts of carbon dioxide and extraction generates methane, both of which are more abundant in the earth's atmosphere than they have been in 800,000 years, according to the EPA.