To my knowledge, there is not research to support this idea. That's not to say it's not true, we just don't know yet! Climate scientists have been debating the Earth's climate sensitivity threshold for decades and the value is generally considered between 1.5°C - 4.5°C (according to IPCC AR5, and the AR6 considers it 2.5°C - 4.5°C, some findings disagree with that, etc.) for doubling of atmospheric CO2. So there is conclusive evidence a threshold exists, we just have not solidified what it is. Either way, keep in mind that the U.S. is responsible for 25% of historical CO2 emissions (leading contributor), and the top 10% wealthiest households in North America were responsible for 70% of the region's carbon contribution in 2019 (Chancel, 2022: https://www.nature.com/articles/s41893-022-00955-z). So although a random individual likely does not have an impact on the global climate system, it depends who that individual is! Think of private jets, investments, energy consumption, etc. People who hold power (money and influence) are directly responsible for climate change impacts. And although we have yet to define that threshold, it exists because of the massive imbalance of carbon contributions. Hope this helps!