Final answer:
Scientists have linked human actions to climate change through discoveries such as the analysis of ice cores revealing historical greenhouse gas levels, tree rings indicating past climate conditions, and understanding the enhanced greenhouse effect from human-caused emissions.
Step-by-step explanation:
Three significant discoveries that have helped scientists understand humans' roles in the planet's climate include:
- Analysis of ice cores provides a historical record of past climates, showing levels of greenhouse gases like CO2 and methane, thus linking human activities, such as the burning of fossil fuels, with the increase in these gases in the atmosphere.
- Study of tree rings (dendrochronology) offers insights into past climatic conditions; changes in ring widths can be associated with variations in temperature and rainfall influenced by human actions over the centuries.
- Understanding the enhanced greenhouse effect caused by the increased concentration of greenhouse gases due to human activities, chiefly the burning of fossil fuels and deforestation, leading to a consensus that these activities are driving recent global warming trends.
These discoveries have strengthened the scientific consensus that current climate changes are not solely due to natural causes but are significantly influenced by human actions, in particular since the mid-20th century.