What surprises lurk within the climate system?

IOPscience: "For generations, our civilization has been building a climate debt, borrowing from the stability of the future to power the economic growth of the present. Through the combustion of fossil fuels, as well as agriculture, deforestation, land use change, and waste, human activities have disrupted the natural carbon cycle, increasing atmospheric carbon dioxide (CO2) by almost 50% and methane (CH4) by 250% relative to pre-industrial levels [2]. Even as this climate debt continues to grow, it is now coming due: the heat trapped by these and other greenhouse gases is raising global temperature, affecting heat and cold extremes, heavy precipitation and drought, sea ice and ice sheet melt, sea level rise and coastal flooding, and many other aspects of the climate system [3] that can harm human health, the economy, food supply, water availability, and even national security [4–6]."