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https://hubblesite.org

Sustainability

· 6 checks — CO2 emissions, green hosting, repeat-visit weight, carbon budget, and transfer efficiency rolled into one auditable list.
SCORE
56
GRADE
D
FIX
3
REVIEW
1
PASS
2
INFO
0
Device:
Mobile Desktop
Checks
6
2 PASS 1 REVIEW 3 FIX
F
CO2 Per Page Load
Action
10.46g CO2 per view
FIX
10.46g CO2 per view
Critical::
10.46g CO2 per page view
This page transfers 36.9 MB, producing an estimated 10.46g of CO2 per visit using the Sustainable Web Design model (v4). Breakdown: data center 1.94g, network 1.81g, end-user device 6.71g.
Got: 10.46g CO2 Expected: < 0.50g (sustainability target)
Info::
At 10,000 monthly views: 1254.8 kg CO2/year
With 10,000 page views per month, this page would generate approximately 1254.8 kg of CO2 annually — equivalent to charging 156854 smartphones.

10.46g

Carbon Footprint per page view

✗ Above sustainability target (0.50g)

Cleaner than 5% of websites

Sustainable Web Design model v4 · Page size: 36.9 MB

Your site
10.46g
Top 10%
0.20g
Target
0.50g
Median website
0.60g

Energy Breakdown

Data center
1.94g
Network
1.81g
End-user device
6.71g
At 10,000 monthly views: Monthly: 104.6 kg · Annual: 1254.8 kg · ≈ 156854 smartphone charges
D
Green Hosting
Action
Unknown
FIX
Unknown
Info::
Hosting provider could not be identified
Without knowing the provider, we cannot determine their energy sourcing. Check with your hosting provider about their renewable energy commitments.
Info::
Green hosting status based on known provider commitments
Green hosting detection uses a curated database of provider renewable energy commitments. This is not a real-time verification. For authoritative checks, visit thegreenwebfoundation.org.
Green HostingUnable to Determine
Hosting Not identified✗CDN Not identified✗

Based on known provider commitments. Verify at thegreenwebfoundation.org

F
Carbon Budget
Action
95th percentile
FIX
95th percentile
Warning::
10.46g CO2 — above the median website (0.60g)
Heavier than an estimated 5% of websites. Reducing page weight, optimizing images, and removing unused JavaScript would lower the carbon footprint. See the Performance tab.
Info::
Estimated 95th percentile
Compared to: top 10% = 0.20g, target = 0.50g, median = 0.60g per page view.
Top 10%
Target
Median website

10.46g

95th percentile

Cleaner than 5% of websites

✗ Above the median website

vs Median 1643% more
vs Target 1991% more
C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

A+
Repeat Visit Weight
100% cached
PASS
100% cached
Info::
100% reduction on repeat visits
Returning visitors download only 158 KB (vs 37810 KB first visit). 116 of 119 resources are served from browser cache, saving 10.41g CO2 per repeat visit.
Info::
Repeat visit: 0.04g CO2 (first visit: 10.46g)
First visit
37810 KB
Repeat visit
158 KB

100% reduction on repeat visits

Saving 10.41g CO2 per returning visitor

116 resources served from cache · 3 resources re-downloaded

A+
Transfer Efficiency
98% efficient
PASS
98% efficient
Info::
Transfer efficiency: 98%
Only 712 KB of potential savings identified. Your page is well-optimized for size.
98% efficient

Total waste: 712 KB (2% of page weight)

Unused JS 712 KB

0.20g unnecessary CO2 per visit

Actual transfer 37810 KB
Theoretical minimum 37097 KB
Potential savings 712 KB (0.20g CO2)

See Deep Analysis sections above for specific optimizations.

All checks on this page are automated. Results are estimates - run targeted manual reviews when the score affects a release decision.

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