1 - Where Do We Stand on Climate Change?

Summary

This is our climate change status check, and the first three things to understand are that climate change is real, anthropogenic (i.e., caused by humans), and dangerous. To drive home those points, this chapter relies heavily on the science of the landmark IPCC climate assessments and particularly the most recent AR5 report. We drill down on a key figure from the AR5 to clarify the observed data since 1850 in respect of global average surface temperatures, sea level rise, atmospheric concentrations of several greenhouse gases, and annual CO₂ emissions. With a second figure we examine the sources of climate forcing since 1950 and clarify the degree to which they are caused by humanity or by nature. We then divert to key facets that we don’t yet fully understand about climate change, including tipping points, “climate sensitivity” and the likely emissions pathway that humanity will choose over the remainder of the century. We conclude with the observation that irrespective of how these mysteries play out, substantial climate change is in our future. It’s coming.