Not working - using earthkit to download CMIP6 data

[nicoler-23]

No longer a bug report, instead a suggested improvement

What happened?

I am trying to download some NetCDF data from the CDS using Earthkit. When downloading the CMIP6 data I need, I get a folder with 3 files:

1. provenance.json
2. provenance.png
3. tasmax_day_CMCC-ESM2_ssp585_r1i1p1f1_gn_20800101-20801231.nc

Earthkit then tries to read all these files, resulting in a warning message "Unknown file type, no reader available." followed by a file path to a .png file. It does correctly load the NetCDF file from the ZIP into memory and I can use it, but it seems like undesired behavior for it to try to load a PNG file (and potentially others) when I am specifying NetCDF.

I have tested this for multiple cases. Below are the example cases I have tried:

These examples threw the same warning

import earthkit.data

# Define request
dataset = "projections-cmip6"
request = {
    'format': 'netcdf',
    'temporal_resolution': 'daily',
    'variable': "daily_maximum_near_surface_air_temperature",
    'experiment': "ssp5_8_5",
    'model': 'cmcc_esm2',
    'year': "2080",
    'month': "01",
    'day': "01",
}

# Download data
ds = earthkit.data.from_source("cds", dataset, request)

Warning: this is 700 MB

import earthkit.data

# Define request
dataset =  "multi-origin-c3s-atlas",                           
request =  {
    "origin": "cmip5",
    "experiment": "historical",
    "domain": "global",
    "period": "1850-2005",
    "variable": "monthly_heavy_precipitation_days",
    "bias_adjustment": "no_bias_adjustment"
    }

# Download data
ds = earthkit.data.from_source("cds", dataset, request)

This did work without the warning

import earthkit.data

# Define request
dataset = "projections-cmip5-daily-pressure-levels",
request =  {
   "experiment": "historical",
    "variable": ["geopotential_height"],
    "model": "access1_0",
    "ensemble_member": "r1i1p1",
    "period": ["19900101-19941231"]
}

# Download data
ds = earthkit.data.from_source("cds", dataset, request)

Note: The example in this link gives the same warning: https://github.com/ecmwf/earthkit-plots/blob/develop/docs/examples/gallery/time-series/cmip6.ipynb

Note the following block of code does this but only reads the NetCDF using cdsapi.

# This code works 
# This code works 
from pathlib import Path
import cdsapi
import os
import xarray as xr
import zipfile

c = cdsapi.Client()  # Key set up in .cdsapirc file

# Define request
dataset = "projections-cmip6"
request = {
    'format': 'zip',
    'temporal_resolution': 'daily',
    'variable': "daily_maximum_near_surface_air_temperature",
    'experiment': "ssp5_8_5",
    'model': 'cmcc_esm2',
    'year': "2080",
    'month': "01",
    'day': "01",
}

# Define filenames
dest = Path('./data')
os.makedirs(dest, exist_ok=True)
zip_path = dest / f"{dataset}_example.zip"
extract_path = zip_path.with_suffix("")

# Download data
c.retrieve(dataset, request, zip_path)

# Manually extract NetCDF file from ZIP
# Based on https://github.com/ecmwf-projects/c3s-atlas/blob/main/c3s_atlas/utils.py
with zipfile.ZipFile(zip_path , 'r') as zip_ref:
    # Get filename inside ZIP
    names = zip_ref.namelist()  # In this example we know we're only downloading one
    name_nc = [filename for filename in names if filename[-3:] == ".nc"][0]

    # Extract
    zip_ref.extract(name_nc, extract_path)

# Open dataset
ds = xr.open_dataset(extract_path/name_nc)
 

What are the steps to reproduce the bug?

import earthkit.data

# Define request
dataset = "projections-cmip6"
request = {
    'format': 'netcdf',
    'temporal_resolution': 'daily',
    'variable': "daily_maximum_near_surface_air_temperature",
    'experiment': "ssp5_8_5",
    'model': 'cmcc_esm2',
    'year': "2080",
    'month': "01",
    'day': "01",
}

# Download data
ds = earthkit.data.from_source("cds", dataset, request)

Version

v0.11.2

Platform (OS and architecture)

Microsoft Windows 11 Enterprise 64-bit operating system, x64-based processor

Relevant log output

2025-08-12 13:36:44,084 INFO [2024-09-26T00:00:00] Watch our [Forum](https://forum.ecmwf.int/) for Announcements, news and other discussed topics.
2025-08-12 13:36:44,356 INFO [2024-09-26T00:00:00] Watch our [Forum](https://forum.ecmwf.int/) for Announcements, news and other discussed topics.
2025-08-12 13:36:45,168 INFO Request ID is 148d75e9-1a82-405b-89b5-caa1b1cd1208
2025-08-12 13:36:45,324 INFO status has been updated to accepted
2025-08-12 13:37:07,031 INFO status has been updated to successful
Unknown file type, no reader available. path=C:\Users\nr2\AppData\Local\Temp\tmpmeer6lxa\cds-d1477e4d87135c5a2a0dd362385cfa389fcf1e9d27c7d2c11c7d82684b59b703.d\provenance.png magic=b'\x89PNG\r\n\x1a\n\x00\x00\x00\rIHDR\x00\x00\n\xd3\x00\x00\x03"\x08\x02\x00\x00\x00\x99\xec9+\x00\x00\x00\x06bKGD\x00\xff\x00\xff\x00\xff\xa0\xbd\xa7\x93\x00\x00 \x00IDATx\x9c\xec\xddw' content_type=None

Accompanying data

No response

Organisation

No response

[sandorkertesz]

@nicoler-23, thank you for reporting this issue. The code will be changed, so when the request contains a type specifier e.g. format': 'netcdf, earthkit-data will not generate these warnings.