climate_science_primer   278

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Disappearing Winter Snowpack | NEEF
April snowpack in the Western United States has decreased by about 23% since 1955.
By 2050, snowmelt in the Northwest US is expected to occur three to four weeks earlier than the 20th century average.
climate_science_primer  snowpack  factoid 
february 2019 by huntercutting
Climate change is making California's fires bigger
“We've been lengthening fire season by shortening the precipitation season, and we're warming throughout,” says Swain. “That's essentially what’s enabled these recent fires to be so destructive, at times of the year when you wouldn't really expect them.”

The total number of wildfires in California hasn’t increased; in fact the numbers were a lot higher in the 1980s and 1990s than in the past decade. The total acreage burned fluctuates considerably from year to year, depending on many factors, including luck: Rain dampens things down early, or fires start in places where they are easier to contain.



Over the past century, California has warmed by about three degrees Fahrenheit. That extra-warmed air sucks water out of plants and soils, leaving the trees, shrubs, and rolling grasslands of the state dry and primed to burn.

That vegetation-drying effect compounds with every degree of warming, explains Daniel Swain, a climate scientist at the University of California, Los Angeles, meaning that plants lose their water more efficiently today than they did before climate change ratcheted up California's temperatures.
California  wildfires  climate_science_primer 
january 2019 by huntercutting
"I wish it weren't a Republican versus Democrat thing": Wildfire photographer Stuart Palley on climate change and California's devastating blazes: Digital Photography Review
in a warming climate we have more days per year that support large fire growth. We have hotter days in the summer that are drying up the vegetation more quickly, which makes them more susceptible to burning. That’s measured using something called the Burn Index. They measured the area around the Camp Fire in Northern California and the Burn Index was 241. It was one of the highest burn indexes ever recorded.
wildfires  climate_science_primer 
november 2018 by huntercutting
CA wildfire start in the woods. Why do cities keep burning? | The Sacramento Bee
California’s WUI zone grew 20 percent from 1990 to 2010, according to U.S. Forest Service data.

Wilderness Urban interface
wildfires  climate_science_primer 
november 2018 by huntercutting
Understanding, modeling and predicting weather and climate extremes: Challenges and opportunities - ScienceDirect
Sillman et al 2017

Abstract

Weather and climate extremes are identified as major areas necessitating further progress in climate research and have thus been selected as one of the World Climate Research Programme (WCRP) Grand Challenges. Here, we provide an overview of current challenges and opportunities for scientific progress and cross-community collaboration on the topic of understanding, modeling and predicting extreme events based on an expert workshop organized as part of the implementation of the WCRP Grand Challenge on Weather and Climate Extremes. In general, the development of an extreme event depends on a favorable initial state, the presence of large-scale drivers, and positive local feedbacks, as well as stochastic processes. We, therefore, elaborate on the scientific challenges related to large-scale drivers and local-to-regional feedback processes leading to extreme events. A better understanding of the drivers and processes will improve the prediction of extremes and will support process-based evaluation of the representation of weather and climate extremes in climate model simulations. Further, we discuss how to address these challenges by focusing on short-duration (less than three days) and long-duration (weeks to months) extreme events, their underlying mechanisms and approaches for their evaluation and prediction.c
climate_modeling  attribution  extremeweather  climate_science_primer 
october 2018 by huntercutting
Carbon Budgets - Carbon Brief
The first is the snappily-titled “threshold exceedance budget”, or “TEB” for short. These are the type used for the “Complex models, RCP only scenarios” rows in the IPCC table.

To calculate a TEB, scientists simulate global temperatures in Earth system models according to a pathway of future emissions that considers all greenhouse gases. Scientists run the model until global temperature rise crosses a given threshold – say 1.5C. They then work out the cumulative CO2 in the atmosphere at that point – and this is the carbon budget.

The other gases are, therefore, taken into account when calculating how the Earth’s climate reached 1.5C of warming, but the resulting budget is still only expressed in CO2.

Of course, this assumes that emissions stop immediately once the threshold temperature is reached, which is essentially impossible in the real world. It also assumes there is no further warming once emissions have stopped, yet recent research shows this isn’t the case, says Dr Joeri Rogelj, a research scholar at the Energy Program of the International Institute for Applied Systems Analysis (IIASA), who is lead author on the Nature Climate Change study. He explains to Carbon Brief:
“This means these budgets are a bit of an overestimate of the carbon we have left to burn because temperatures would continue to warm for about a decade after we stopped emitting CO2.”

The TEB is the approach used to calculate the carbon budget we presented above. In the IPCC’s calculations, they assume emissions continue along the RCP8.5 pathway – where greenhouse gas emissions aren’t curbed – and simulate the impact on global temperatures in 20 different models.

The second approach for carbon budgets that take other gases into account is the “TAB”, or “Threshold Avoidance Budget”. These are the type used for the “Simple model, WGIII scenarios” rows in the IPCC table above.

In calculating TABs, scientists simulate many scenarios in a simple model and only pick scenarios that don’t exceed the temperature in question. From these scenarios, they then estimate a carbon budget for staying below that temperature.

Therefore, rather than using one scenario in lots of models, the TAB approach uses lots of scenarios in one model.

So, both the TEB and TAB approach to calculating carbon budgets have their strengths and weaknesses. But which one will scientists favour for future IPCC reports? Rogelj suggests both:

“I expect we will continue to use both in the future. However, to inform policymaking, it makes most sense to derive carbon budgets from scenarios that actually limit warming to below a particular temperature limit.”
CarbonBudget  climate_science_primer 
september 2018 by huntercutting
AP Explains: Driven by climate change, fire reshapes US West
The time interval between wildfires in some locations is getting shorter, even as there’s less moisture to help trees regrow. That means some forests burn, then never grow back, converting instead into shrub land more adapted to frequent fire, said Jonathan Thompson, a senior ecologist at Harvard University.

“They get stuck in this trap of repeated, high-severity fire,” Thompson said. “Through time we’ll see the California shrub land shifting north.”
wildfires  climate_science_primer 
september 2018 by huntercutting

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