A paper published in Geophysical Research Letters discusses the trend of dissolved O2 in the upper-ocean. The authors studied dissolved O2 levels in the world's oceans for the period of 1955 to 2015 and stated,
After careful examination of the data, we found that a statistically significant, widespread O2 decline is emerging beyond the envelope of natural fluctuations. Our study also reveals a tight relationship between O2 inventories and the ocean heat content.This, of course should disturb anyone reading it. They did not indicate that the oxygen levels are becoming dangerous. But, if there is a trend of decreasing dissolved O2 in the world's oceans, there will be areas were the O2 level is, in fact, depleted to dangerous levels. There are already hypoxic areas - known as 'dead zones' - in the oceans where the O2 level is so low most marine life either dies or leaves the area. These areas are principally caused by excessive nutrient pollution coupled with other factors. If the O2 level is depleted by additional, other means, then these dead zones will increase in both number and extent. Since all life on the planet is dependent on marine life, this is something we need to be paying attention to.
By the way, the authors found "The spatial pattern and magnitude of this relationship are consistent with expectations derived from mechanistic ocean climate models forced under climate warming scenarios" That would be the same climate change the anti-science people claim isn't happening.
Another paper, published in Global Biogeochemical Cycles (published by the AGU) discussed the levels of methane in the air. The authors examined the atmospheric methane levels since the early-1980s with an emphasis on the period since the year 2000. What they found is that there has been a large increase in atmospheric methane since 2007. Interestingly, the isotopic ratios indicate this increase is not due to fossil fuels. Rather, their analysis indicates it comes from wetlands and agriculture. What is disturbing is their conclusion:
The scale and pace of the present methane rise (roughly 60 ppb in 9 years since the start of 2007), and the concurrent isotopic shift showing that the increase is dominantly from biogenic sources, imply that methane emission (both from natural wetlands and agriculture) is responding to sustained changes in precipitation and temperature in the tropics. If so, is this merely a decadal-length weather oscillation, or is it a troubling harbinger of more severe climatic change? Is the current sustained event in the normal range of meteorological fluctuation? Or is a shift occurring that is becoming comparable in scale to events recorded in ice cores [Wolff and Spahni, 2007; Möller et al., 2013; Sperlich et al., 2015]? In the past millennium between 1000 and 1700 C.E., methane mole fraction varied by no more than about 55 ppb [Feretti et al., 2005]. Methane in past global climate events has been both a “first indicator” and a “first responder” to climatic change [Severinghaus and Brook, 1999; Möller et al., 2013; Etheridge et al., 1998]. Comparison with these historic events suggests that if methane growth continues, and is indeed driven by biogenic emissions, the present increase is already becoming exceptional, beyond the largest events in the last millennium.
Methane, they state, has been both a first indicator and a first responder and the current increase is already beyond the largest events of the last millennium. Wow.
The science is indeed settled. Manmade emissions and activities are changing the climate. What is not settled is just what that means to us and how much damage is being done. These two papers show us some of the damage that is being done right now and the news is not good.