Global Mean Surface Temperature Anomalies (GMSTA) from CMIP6 data

Overview¶

In this notebook we will compute the Global Mean Surface Temperature Anomalies (GMSTA) from CMIP6 data and compare it with observations. This notebook is heavily inspired by the GMST example in the CMIP6 cookbook and we thank the authors for their workflow.

We will get the CMIP6 temperature data from the AWS open data program via the us-west-2 origin
In order to do this, we will use an intake-ESM catalog (hosted on NCAR’s GDEX) that uses pelicanFS backed links instead of https or s3 links
We will grab observational data hosted on NCAR’s GDEX, which is accessible via the NCAR origin
Please refer to the first chapter of this cookbook to learn more about OSDF, pelican or pelicanFS
This notebook demonstrates that you can seamlessly stream data from multiple OSDF origins in your workflow

Prerequisites¶

Concepts	Importance	Notes
Intro to Intake-ESM	Necessary	Used for searching CMIP6 data
Understanding of Zarr	Helpful	Familiarity with metadata structure
Seaborn	Helpful	Used for plotting
PelicanFS	Necessary	The python package used to stream data in this notebook
OSDF	Helpful	OSDF is used to stream data in this notebook

Time to learn: 20 mins

Imports¶

from matplotlib import pyplot as plt
import xarray as xr
import numpy as np
from dask.diagnostics import progress
from tqdm.autonotebook import tqdm
import intake
import fsspec
import seaborn as sns
import aiohttp
import dask
from dask.distributed import LocalCluster
import pelicanfs

/tmp/ipykernel_4109/2849986847.py:5: TqdmWarning: IProgress not found. Please update jupyter and ipywidgets. See https://ipywidgets.readthedocs.io/en/stable/user_install.html
  from tqdm.autonotebook import tqdm

We will use an intake-ESM catalog hosted on NCAR’s Geoscience Data Exchange. This is nothing but the AWS cmip6 catalog modified to use OSDF

# Load catalog URL
gdex_url    =  'https://data.gdex.ucar.edu/'
cat_url     = gdex_url +  'd850001/catalogs/osdf/cmip6-aws/cmip6-osdf-zarr.json'
print(cat_url)

https://data.gdex.ucar.edu/d850001/catalogs/osdf/cmip6-aws/cmip6-osdf-zarr.json

Set up local dask cluster¶

Before we do any computation let us first set up a local cluster using dask

cluster = LocalCluster()          
client = cluster.get_client()

/home/runner/micromamba/envs/osdf-cookbook/lib/python3.12/site-packages/distributed/node.py:188: UserWarning: Port 8787 is already in use.
Perhaps you already have a cluster running?
Hosting the HTTP server on port 46131 instead
  warnings.warn(

# Scale the cluster
n_workers = 3
cluster.scale(n_workers)
cluster

Data Loading¶

Load CMIP6 data from AWS¶

col = intake.open_esm_datastore(cat_url)
col

# there is currently a significant amount of data for these runs
expts = ['historical', 'ssp245', 'ssp370']

query = dict(
    experiment_id=expts,
    table_id='Amon',
    variable_id=['tas'],
    member_id = 'r1i1p1f1',
    #activity_id = 'CMIP',
)

col_subset = col.search(require_all_on=["source_id"], **query)
col_subset

Let us inspect the zarr store paths to see if we are using the pelican protocol.
We see that zstore column has paths that start with ‘osdf:///’ instead of ‘https://’ which tells us that we are not using a simple ‘https’ GET request to fetch the data.
In order to know more about the pelican protocol, please refer to the first chapter of this cookbook.

col_subset.df

Grab some Observational time series data for comparison with ensemble spread¶

The observational data we will use is the HadCRUT5 dataset from the UK Met Office
The data has been downloaded to NCAR’s Geoscience Data Exchange (GDEX) from https://www.metoffice.gov.uk/hadobs/hadcrut5/
We will use an OSDF to access this copy from the GDEX. Again the links will start with ‘osdf:///’

%%time
obs_url    = 'osdf:///ncar/gdex/d850001/HadCRUT.5.0.2.0.analysis.summary_series.global.monthly.nc'
#
obs_ds = xr.open_dataset(obs_url, engine='h5netcdf').tas_mean
obs_ds

CPU times: user 1.53 s, sys: 172 ms, total: 1.7 s
Wall time: 2.93 s

Some helpful functions¶

def drop_all_bounds(ds):
    drop_vars = [vname for vname in ds.coords
                 if (('_bounds') in vname ) or ('_bnds') in vname]
    return ds.drop_vars(drop_vars)

def open_dset(df):
    assert len(df) == 1
    mapper = fsspec.get_mapper(df.zstore.values[0])
    #path = df.zstore.values[0][7:]+".zmetadata"
    ds = xr.open_zarr(mapper, consolidated=True)
    return drop_all_bounds(ds)

def open_delayed(df):
    return dask.delayed(open_dset)(df)

from collections import defaultdict
dsets = defaultdict(dict)

for group, df in col_subset.df.groupby(by=['source_id', 'experiment_id']):
    dsets[group[0]][group[1]] = open_delayed(df)

dsets_ = dask.compute(dict(dsets))[0]

#calculate global means
def get_lat_name(ds):
    for lat_name in ['lat', 'latitude']:
        if lat_name in ds.coords:
            return lat_name
    raise RuntimeError("Couldn't find a latitude coordinate")

def global_mean(ds):
    lat = ds[get_lat_name(ds)]
    weight = np.cos(np.deg2rad(lat))
    weight /= weight.mean()
    other_dims = set(ds.dims) - {'time'}
    return (ds * weight).mean(other_dims)

#calculate global means
def get_lat_name(ds):
    for lat_name in ['lat', 'latitude']:
        if lat_name in ds.coords:
            return lat_name
    raise RuntimeError("Couldn't find a latitude coordinate")

def global_mean(ds):
    lat = ds[get_lat_name(ds)]
    weight = np.cos(np.deg2rad(lat))
    weight /= weight.mean()
    other_dims = set(ds.dims) - {'time'}
    return (ds * weight).mean(other_dims)

GMST computation¶

expt_da = xr.DataArray(expts, dims='experiment_id', name='experiment_id',
                       coords={'experiment_id': expts})

dsets_aligned = {}

for k, v in tqdm(dsets_.items()):
    expt_dsets = v.values()
    if any([d is None for d in expt_dsets]):
        print(f"Missing experiment for {k}")
        continue

    for ds in expt_dsets:
        ds.coords['year'] = ds.time.dt.year

    # workaround for
    # https://github.com/pydata/xarray/issues/2237#issuecomment-620961663
    dsets_ann_mean = [v[expt].pipe(global_mean).swap_dims({'time': 'year'})
                             .drop_vars('time').coarsen(year=12).mean()
                      for expt in expts]

    # align everything with the 4xCO2 experiment
    dsets_aligned[k] = xr.concat(dsets_ann_mean, join='outer',dim=expt_da)

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%%time
with progress.ProgressBar():
    dsets_aligned_ = dask.compute(dsets_aligned)[0]

CPU times: user 11.8 s, sys: 2 s, total: 13.8 s
Wall time: 2min 21s

source_ids = list(dsets_aligned_.keys())
source_da = xr.DataArray(source_ids, dims='source_id', name='source_id',
                         coords={'source_id': source_ids})

big_ds = xr.concat([ds.reset_coords(drop=True)
                    for ds in dsets_aligned_.values()],
                    dim=source_da)

big_ds

/tmp/ipykernel_4109/2886188115.py:5: FutureWarning: In a future version of xarray the default value for join will change from join='outer' to join='exact'. This change will result in the following ValueError: cannot be aligned with join='exact' because index/labels/sizes are not equal along these coordinates (dimensions): 'year' ('year',) The recommendation is to set join explicitly for this case.
  big_ds = xr.concat([ds.reset_coords(drop=True)

# Compute annual mean temperatures anomalies of observational data
obs_gmsta = obs_ds.resample(time='YS').mean(dim='time')
# obs_gmsta

Compute anomlaies and plot¶

We will compute the temperature anomalies w.r.t 1960-1990 baseline period
Convert xarray datasets to pandas dataframes
Use Seaborn to plot GMSTA

df_all = big_ds.to_dataframe().reset_index()
df_all.head()

# Define the baseline period
baseline_df = df_all[(df_all["year"] >= 1960) & (df_all["year"] <= 1990)]

# Compute the baseline mean
baseline_mean = baseline_df["tas"].mean()

# Compute anomalies
df_all["tas_anomaly"] = df_all["tas"] - baseline_mean
df_all

obs_df = obs_gmsta.to_dataframe(name='tas_anomaly').reset_index()

# Convert 'time' to 'year' (keeping only the year)
obs_df['year'] = obs_df['time'].dt.year

# Drop the original 'time' column since we extracted 'year'
obs_df = obs_df[['year', 'tas_anomaly']]
obs_df

Almost there! Let us now use seaborn to plot all the anomalies

g = sns.relplot(data=df_all, x="year", y="tas_anomaly",
                hue='experiment_id', kind="line", errorbar="sd", aspect=2, palette="Set2")  # Adjust the color palette)

# Get the current axis from the FacetGrid
ax = g.ax

# Overlay the observational data in red
sns.lineplot(data=obs_df, x="year", y="tas_anomaly",color="red", 
             linestyle="dashed", linewidth=2,label="Observations", ax=ax)

# Adjust the legend to include observations
ax.legend(title="Experiment ID + Observations")

# Show the plot
plt.show()

Summary¶

In this notebook, we used surface air temperature data from several CMIP6 models for the ‘historical’, ‘SSP245’ and ‘SSP370’ runs to compute Global Mean Surface Temperature Anomaly (GMSTA) relative to the 1960-1990 baseline period and compare it with anomalies computed from the HadCRUT monthly surface temperature dataset. We used a modified intake-ESM catalog and pelicanFS to ‘stream/download’ temperature data from two different OSDF origins. The CMIP6 model data was streamed from the AWS OpenData origin in the us-west-2 region and the observational data was streamed from NCAR’s OSDF origin.

Resources and references¶

Original notebook in the Pangeo Gallery by Henri Drake and Ryan Abernathey
CMIP6 cookbook by Ryan Abernathey, Henri Drake, Robert Ford and Max Grover
Coupled Model Intercomparison Project 6 was accessed from https://registry.opendata.aws/cmip6 using a modified intake-ESM catalog hosted on NCAR’s GDEX
We thank the UK Met Office Hadley Center for providing the observational data