Global Mean Atmospheric CO2 Levels Clear 400ppm, Forever: The average concentration of carbon dioxide in our atmosphere fluctuates annually, dropping during the northern hemisphere’s spring and summer and rising in the fall and winter. This pattern is a product of what ecologists refer to as the phenology of northern forests: the timing of key events in their life cycle. As deciduous trees grow new leaves in spring, they increase their capacity to store carbon dioxide and steadily remove it from the atmosphere. Then, as these leaves fall to the ground and decompose prior to the onset of winter, carbon dioxide is re-released, causing concentrations to spike. And so while we’ve exceeded concentrations of 400 parts per million in the recent past, levels have always dropped back down to a more comforting 350-399 ppm average during the September, the cycle’s annual nadir. No longer: for the first time in recorded history, CO2 concentrations remained above 400 ppm for the entire month—meaning they’re unlikely to ever fall below this symbolic milestone again. Climate Central has more.

But That Doesn’t Mean We Will Warm The Earth 13 Degrees F: In a letter in the journal Nature this month, Stanford University’s Carol Snyder presents a highly detailed history of global average surface temperatures (or GAST) over the past two million years. Snyder’s reconstruction relies on computer simulations and temperature records from oceanic sediment cores, and has been widely accepted as a valuable contribution to our understanding of global climate history. But one of the most eye-popping conclusions in the paper — the prediction that even if we managed to cap fossil fuel emissions at their current level, the planet is doomed to a dramatic 13 degrees Fahrenheit increase in GAST—has come under scrutiny from other scientists, who claim this deduction isn’t supported by the data. As UW’s Eric Steig put it to National Geographic: "She's making a statement about the future, but I don't find anything in the paper that explains why she thinks she can do that."

The Blob, Though, Continues To Haunt Us, Causing Unprecedented Algae Blooms: Last year, the northeastern Pacific Ocean was the site of both a persistent region of anomalously warm water (“The Blob”) and a massive toxic algae bloom. Now, researchers at University of Washington have linked the two events, publishing a paper in the journal Geophysical Research Letters that claims the Blob’s influence on ocean temperatures and local weather triggered the conditions necessary for high algae growth rates.

Science Event of (Next) Week: On Saturday, October 8th, the Burke Museum will be hosting its annual “Bird at the Burke” event, featuring talks, games, and displays from the research division’s ornithology collections. I’ll be there all day, working with specimens — feel free to stop by and say hi.