The average global temperature fluctuates every year. However, when you look at a snapshot of the global temperature trend, it's on the rise - particularly since 1970. The main cause? Carbon dioxide and other greenhouse gas emissions from human activities.
There are plenty of factors that influence temperatures in different regions across the globe. El Niño is one of the biggest drivers of year-to-year variability, increasing the likelihood of warm weather in the Pacific Northwest and cooler weather in the Southeast as well as a host of other global impacts. Longer-term fluctuations such as the Pacific Decadal Oscillation and aerosols from natural and human sources can further affect regional climate. Solar cycles also have global temperature implications, although on a much smaller scale.
These shifts taken individually and together account for the year-to-year variability seen in the global average temperatures. They can’t fully explain why the globe has warmed about 1.6°F since 1880, though.
Overlaying the amount of carbon dioxide in the atmosphere shows a clear correlation with that rise in temperatures. Of course correlation doesn’t always equal causation.
However, reams of peer-reviewed research, basic physics, the ability to track the specific chemical fingerprint of fossil fuel-driven carbon, and the fact that no models can replicate this century's warming without pumping up carbon dioxide and other greenhouse gases in the atmosphere give scientists confidence that human carbon emissions are driving the globe’s temperature higher. Other indicators such as ocean acidification, increasing deep ocean heat, melting ice and permafrost, shrinking snow pack, and sea level rise further make the case that the additional carbon dioxide is affecting the global climate system.
There are periods when other factors might temporarily slow that rise such as the much-discussed global warming “pause” of the last decade, but the overall connection is clear. If greenhouse gas emissions continue to rise, the globe’s average temperature is projected to follow suit. The worst-case emissions scenario, the track that we are currently on, estimates a rise in temperature of 4.7° to 8.6°F by 2100. International negotiators are at a meeting in Warsaw that continues through November 22 in an effort to lay the groundwork for a global climate treaty that aims to limit the temperature from rising more than 3.6°F above pre-industrial levels.