Final answer:
Dr. Katharine Hayhoe identified four 'usual suspects' that have contributed to past climate changes. Human activities, particularly the combustion of fossil fuels, are the primary cause of current climate changes.
Step-by-step explanation:
Dr. Katharine Hayhoe, a climate scientist, has identified four 'usual suspects' that have contributed to changes in climate in the past. These suspects are:
- Changes in solar energy
- Volcanic eruptions
- Natural changes in greenhouse gas (GHG) concentrations
- Continental drift
However, it is important to note that the science indicates that the current climate changes cannot be solely explained by natural causes. Human activities, particularly the combustion of fossil fuels, are the primary driving force behind the climate changes we are experiencing today.