In 2007 the Intergovernmental Panel on Climate Change (IPCC) released their 4^th report stating human caused climate change is ‘unequivocal.’ To understand how a scientific panel can clearly, and with no doubt, make such a statement about carbon dioxide emissions, we need to understand the trends that led to the 2007 IPCC report.

Initially, the increase of CO₂ output was a result of industrialization and populations growth, especially in the United States. Generally, as economies developed and grew between 1850 and 1960, the emissions for each country also grew. Between 1960 and 2011, many countries in Asia started to increase their emissions as well, resulting in China becoming the top emitter in 2005. What is interesting is that in 2007, the CO₂ emissions from developing nations exceeded those of the industrialized ones. The rate of carbon emissions—and the subsequent warming—is the true point of concern. Although, there have been warming periods due to natural causes before (volcanic eruptions, changes in solar energy, etc.), our current warming can’t be explained by natural causes alone. In fact, in the entire history of human civilization, CO₂ levels have never been this high (more than 400ppm).

The climate change that occurs due to these increased emissions has numerous impacts on the environment and humans.  An interesting case study to explore the impacts of global ‘unequivocal’ climate change is the Arctic. In the Arctic, climate change is faster and more severe there than in the rest of the world—warming at almost twice the global average. Scientists observed that arctic sea ice has decreased 14% since the 1970s, and that 2012 had the lowest level of sea ice extent ever recorded.

What does a warming Arctic mean for the rest of the planet? The melting sea ice can cause up to a 1m rise in sea level and impact coastal communities. As the ice melts, the Arctic’s ability to reflect heat back to space becomes reduced, resulting in higher rates of warming in the world. Also, a warmer Arctic could impact the flow or halt of the Gulf Stream, changing the global climate and precipitation patterns.

The National Academies of Science’s Arctic Matters booklet is a great educational resource that explains the threats to the Arctic, as well as why it needs to be a universal concern. On January 14, 2016 the NAS is hosting Arctic Matters Day in Washington, DC—a combination of presentations and discussions to explore the issue. Some great teaching resources, including their booklet and classroom poster, will be available for free at the event or online.

The Environment Timeline on worldpopulationhistory.org offers insights into other, similar milestones throughout history where humans have impacted the Earth.