Final answer:
The highest concentration of greenhouse gases in Earth's atmosphere within the last 400,000 years was present day.
Explanation:
The highest concentration of greenhouse gases in Earth's atmosphere within the last 400,000 years was present day. Data shows that carbon dioxide levels have increased significantly since the Industrial Revolution, with concentrations reaching 409.8 ppm in 2019. Methane, another potent greenhouse gas, is also at its highest levels in at least the past 650,000 years.
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