Blockchain-based Traceability of Carbon Footprint:

A Solidity Smart Contract for Ethereum

Ant

onio Miguel Rosado da Cruz

1,2,∗

, Francisco Santos

, Paulo Mendes

and Estrela Ferreira Cruz

1,2,∗

Instituto Polit

ecnico de Viana do Castelo, 4900-347, Viana do Castelo, Portugal

Centro ALGORITMI, Escola de Engenharia, Universidade do Minho, Guimar

aes, Portugal

Keywords:

Blockchain, Solidity, Smart Contract, Ethereum, Carbon Footprint, Traceability, Monitoring.

Abstract:

In recent decades there has been an increasing concern about climate change. Every person is increasingly

concerned about global warming and, as a consumer, with their own individual contribute to that issue, wich

may be measured by each one’s carbon footprint. In this sense, it is only natural that each person wants

to consume products with a lower carbon footprint, meaning with a lower environmental impact. For this,

however, consumers need to be able to know the carbon footprint of the products they are buying. This is only

possible by having every company tracking and sharing their own products carbon footprint. The blockchain

is a distributed technology that allows for registering and sharing information between those companies and

the ﬁnal consumers. The blockchain is being used in many areas as a distributed database, and has some

strong points like trust, transparency, security, immutability, durability, disintermediation and others. In this

paper the blockchain technology is being used to track and trace back the carbon footprint of products and

organizations. More exactly, this paper proposes a smart contract-based platform for the traceability of the

carbon footprint of products and organizations.

1 INTRODUCTION

Climate change is today one of humanity’s greatest

challenges. Efforts to ﬁght it tend to focus on re-

ducing known causes, such as the concentration of

greenhouse gases in the atmosphere. One of the ma-

jor causes of climate change is the so-called carbon

footprint of mankind. Year 2018 was the year when

the average ocean temperature was highest since the

beginning of recordings, and atmospheric concentra-

tions of greenhouse gases such as carbon dioxide

(CO

), methane (CH

) and nitrous oxide (N

O) were

the highest ever (NOAA, 2019; C3S, 2019). The

growth of these indicators, along with many other di-

rectly or indirectly related indicators, is the reason

why more and more environmental awareness is tak-

ing a prominent role, which it had not a few years ago.

Carbon footprint may be deﬁned as “the amount of

gaseous emissions that are relevant to climate change

(gases with greenhouse effect) and associated with

human production or consumption activities” (Wied-

mann and Minx, 2008). Different greenhouse gases

last in the atmosphere for different amounts of time

∗

Contact Authors.

and absorb different amounts of heat. Carbon foot-

print, measured in carbon dioxide equivalent (CO

e),

allows to describe different greenhouse gases in a

common unit. For any quantity and type of green-

house gas, CO

e refers to the amount of CO

that

would have the equivalent global warming impact

(C3S, 2019). A carbon footprint considers the seven

Kyoto Protocol greenhouse gases: Carbon dioxide

(CO

), Methane (CH

), Nitrous oxide (N

O), Hy-

droﬂuorocarbons (HFCs), Perﬂuorocarbons (PFCs),

Sulphur hexaﬂuoride (SF

) and Nitrogen triﬂuoride

((NF

)

). CO

e is calculated by multiplying the emis-

sions of each of the six greenhouse gases by its 100-

year global warming potential (GWP). The GWP of

is 1, and the GWP for all other greenhouse gases

is the number of times more warming they cause com-

pared to CO

(CarbonTrust, 2019; C3S, 2019).

Wiedmann and Minx mainly discuss two method-

ologies for carbon footprint analysis: process analysis

and input-output analysis. For the assessment of indi-

vidual products, the authors suggest a Hybrid-EIO-

LCA approach (EIO- Environmental input-output,

LCA- Life Cycle Analysis/Assessment), where life-

cycle assessments are combined with input-output

analysis. The authors also noted it is important for

258

Rosado da Cruz, A., Santos, F., Mendes, P. and Cruz, E.

Blockchain-based Traceability of Carbon Footprint: A Solidity Smart Contract for Ethereum.

DOI: 10.5220/0009412602580268

In Proceedings of the 22nd International Conference on Enterprise Information Systems (ICEIS 2020) - Volume 2, pages 258-268

ISBN: 978-989-758-423-7

a carbon footprint to include all direct as well as in-

direct CO

emissions, and it is also “important to

avoid double-counting along supply chains or life cy-

cles” (Wiedmann and Minx, 2008). So, for assess-

ing a product carbon footprint within a value chain,

one needs to measure and store information about car-

bon emissions on every step of the product life cycle,

from conception or production, to transport, storage,

etc. For implementing this, we decided to use the

blockchain technology.

Blockchain is a distributed registration technology

that aims at decentralization as a security measure,

and in which all committed transactions are stored in

a chain of blocks (Zheng et al., 2018). This chain is

constantly growing as new blocks are added to it in

a linear and chronological way. It is a decentralized

system, where each node of the network gets a copy

of the database after joining the network and has the

task of validating and passing on transactions.

Some blockchains, like Ethereum, offer a decen-

tralized virtual machine to handle smart contracts,

which are like digital contracts that control users’ dig-

ital assets, formulating the participants’ rights and

obligations (Lin and Liao, 2017). Ethereum is a de-

centralized platform capable of executing smart con-

tracts and decentralized applications using blockchain

technology. It has a Turing complete decentral-

ized virtual machine, the Ethereum Virtual Machine

(EVM), which can encode rules and run scripts for

processing transactions (Luu et al., 2016).

The blockchain technology is being used as a dis-

tributed and replicated database in many areas (Saberi

et al., 2019; Tian, 2017). The technology has some

strong points like trust, transparency, immutability,

among others (Dujak and Sajter, 2019).

There are three main types of blockchain: per-

missionless public blockchain; permissioned public

blockchain (hybrid blockchain) and permissioned pri-

vate blockchain (closed network) (Pedersen et al.,

2019). Blockchain technologies can be used in many

areas like digital currency (e.g. Ethereum, Bitcoin),

Smart Contract (e.g. Ethereum, Hyperledger), pro-

tection of Intellectual property, Traceability in sup-

ply chain, Identify certiﬁcation, International pay-

ments, Financial services, Risk management, Internet

of things (IoT), etc. (Lin and Liao, 2017).

This paper’s main contribution is to present an ap-

proach to trace and (dynamically) calculate the carbon

footprint of products and organizations, by using a

permissionless public blockchain, namely Ethereum.

The paper also presents a distributed application pro-

viding to consumers information about the carbon

footprint of a product or organization stored in the

blockchain.

The structure of the presentation is as follows: In

the next section, related work is presented, concern-

ing the value chain traceability of carbon footprint

and blockchain-based approaches for traceability of

other product’s properties. Then, in section 3, the con-

ceptualization of the proposed traceability platform of

products’ and organizations’ carbon footprint is de-

scribed. Section 4 reports on the development and

validation of the platform’s smart contract, and sec-

tion 5 addresses the architecture and development of

the blockchain-based distributed application. Section

6 concludes the paper and raises ideas for future work.

2 RELATED WORK

2.1 Tracing Carbon Footprint

It is not easy to ﬁnd articles alluding to the carbon

footprint traceability of a product in the literature.

Some articles present methods for calculating car-

bon emissions, as is the case of (Li et al., 2013).

Li et al. present a method for tracing the carbon

ﬂow to determine carbon emissions obligation from

electricity consumption. In (Cordero, 2013), the au-

thor brieﬂy surveys carbon footprint estimation ap-

proaches within supply chains.

Fu et al. propose a framework to expose the

FAMI (fashion apparel manufacturing industry) car-

bon emissions to the general public and deﬁne a set of

guidelines for reducing carbon emissions at all stages

of manufacturing (Fu et al., 2018). The study starts

by reviewing existing blockchain applications to im-

prove sustainability and then the authors propose a

blockchain based solution to encourage lower carbon

emissions (Fu et al., 2018).

In (Pan et al., 2018) a blockchain-based applica-

tion to carbon trading is proposed.

To our knowledge, there is not in the literature a

proposal presenting a platform for tracing a product’s

carbon footprint using blockchain technology. De-

spite this, the next subsection presents some works

that use the blockchain technology for value chain op-

erational support or location traceability.

2.2 Blockchain-based Treacealility

Platforms

Blockchain technology embraces concepts like de-

centralization, transparency, open source, autonomy,

anonymity and immutability (Lin and Liao, 2017).

It also has some disadvantages, though. Compared

to traditional centralized databases, Blockchains have

Blockchain-based Traceability of Carbon Footprint: A Solidity Smart Contract for Ethereum

259

limited efﬁciency and require larger storage capacity,

leading to poor performance and much higher energy

costs. The blockchain technology can be a great solu-

tion to be used in some situations but it certainly is not

the best solution to be used in all of them. Pedersen et

al. propose a set of ten steps to help in deciding if the

blockchain technology is the best option to a speciﬁc

problem or not, and if so, what kind of blockchain is

a better ﬁt (Pedersen et al., 2019).

In (Deloitte, 2019), Deloitte performed a survey

about integrating blockchain into their business oper-

ations. The study involved around 1,000 big compa-

nies from 12 countries from 4 continents. This sur-

vey, from 2019, concluded that 34% already had a

blockchain system in production and 41% expected

to implement a blockchain application within the next

12 months. The survey concludes that “53% of re-

spondents say that blockchain technology has become

a critical priority for their organizations”. In compar-

ison to the survey previously performed in 2018, the

authors notice a 10-point increase in 2019 over 2018.

Value chain integration and digitization is becom-

ing increasingly important, not only for practical rea-

sons, but also for reasons of transparency and secu-

rity (Cruz and da Cruz, 2019). Korpela et al. research

the supply chain integration and the role played by

blockchain technology in digital supply chain trans-

formations. According to the authors, value chain in-

tegration has advantages for everyone involved: sup-

pliers, customers, intermediaries, etc. The authors

present several advantages such as: increase value

chain efﬁciency; ease of the communication between

chain operators; possibility of tracing the product

since the beginning of the chain; decreased need for

human intervention (automatic data collection) reduc-

ing human error, etc.(Korpela et al., 2017).

In (Saberi et al., 2019), the authors identify some

strengths of the use of blockchain for the integration

of the value chain. Blockchain technology can sup-

port data collection, storage, and management, thus

enabling support for most of the value/supply chains

information. Saberi et al. focus their attention mainly

on the use of blockchain in sustainable supply chains.

According to the authors, blockchain can be used

to: ensure that green products are environmentally

friendly; trace the carbon footprint of a product; im-

prove recycling; improve emission trading schemes

efﬁcacy; etc. (Saberi et al., 2019).

Several authors are using blockchain for traceabil-

ity in food supply chains, as is the case of (Biswas

et al., 2017), (Tan et al., 2019), (Tian, 2017), (Galvez

et al., 2018), (Caro et al., 2018) and others.

Biswas et al. propose a blockchain-based wine

supply chain to record detailed information in order

to trace the origin, production and purchase history of

the wine. The authors designed and implemented a

blockchain with ﬁve entities (one entity for each wine

chain operator) (Biswas et al., 2017). Three of the en-

tities were designed as the miners and all entities in

the chain generate their own blocks containing trans-

actions. These transactions are veriﬁed by the miners

before being added in the chain (Biswas et al., 2017).

Feng Tian proposes a decentralized system based

on IoT and blockchain technology to support trace-

ability in food supply chain (Tian, 2017). The au-

thor identiﬁes a set of advantages and disadvantages

of blockchain databases and proposed a new concept,

named as BigChainDB, by combining the beneﬁts

of distributed databases and blockchain. This way

the author deals with blockchain problems like low

throughput, high latency and scalability (Tian, 2017).

In Galvez et al. the authors main goal is to study

the use of blockchain to store data from chemical

analysis to ensure transparency in food supply chain,

avoiding food falsiﬁcation or adulteration. The au-

thors study the potential of blockchain technology for

assuring traceability and authenticity in the food sup-

ply chain (Galvez et al., 2018). The authors conclude

that the use of blockchain has many advantages in

traceability, such as allowing all stakeholders to check

the entire history and current location of a product;

assures geographic biological origin by collecting in-

formation from sensors and store it directly into the

blockchain(Galvez et al., 2018)..

Caro et al. propose a decentralized solution for

agri-Food supply chain management and traceability

based on blockchain. The presented solution is able

to integrate data produced and consumed by IoT de-

vices. The authors used Ethereum and Hyperledger

Sawtooth blockchains (Caro et al., 2018).

Luu et al. research the security problems of exe-

cuting smart contracts on the Ethereum platform. The

authors identify several vulnerabilities and propose

solutions to overcome them and make contracts more

secure (Luu et al., 2016). They also propose a tool

to identify and alert for potential security ﬂaws when

coding smart contracts (Luu et al., 2016).

3 THE CARBON FOOTPRINT

TRACEABILITY PLATFORM

CONCEPTUALIZATION

Informed people tend to make better, or more con-

scious, choices when presented with various alterna-

tives as long as there is no personal detriment. The

best way to encourage consumers to choose products

ICEIS 2020 - 22nd International Conference on Enterprise Information Systems

260

with the least impact on the environment is to provide

a platform where each consumer may follow the pro-

duction chain of a given product, and verify its prove-

nance, as well as access the quantiﬁcation of the prod-

uct’s impact on the environment.

We believe the trend is for consumers to choose

the most environmentally conscious products, and,

over time, this will lead to a paradigm shift with a big

impact on how we look for and purchase the products

we need. Similarly, organizations would also beneﬁt

from this model, since if their production is the most

environmentally efﬁcient, in addition to contributing

to the well-being of the planet, they may be also con-

tributing to their sales and their image to consumers.

For computing the environmental impact of pro-

ducing a given product, and since not all environmen-

tal costs can be accounted for by the same metric, it

is necessary to use equivalence tables, which convert

to CO

e the greenhouse gases generated by the con-

sumption of certain materials. The CO

e is calculated

based on the global warming potential for the mixture

and amount of greenhouse gases produced by pro-

cessing a particular material. This metric gives us a

standard and comparable way of accounting for the

impact of all production activities, regardless of the

materials used, and eventually reach an absolute value

that can be used for benchmarking. This is called the

carbon footprint of the product, and it is a value that

ﬂuctuates from month to month, from production ac-

tivity to production activity, being recalculated and in-

dexed to each speciﬁc batch/lot of articles produced.

To calculate the carbon footprint of a product, ﬁrst

we need to know the activities involved in its creation

(production), the products used in its production and

their corresponding carbon footprint. For example,

suppose you want to make a yogurt cake. This cake

contains yogurt, eggs, ﬂour, sugar, etc.. In turn, yo-

gurt needs milk, strawberry, etc.. Each involved prod-

uct has its own carbon footprint. This may be rep-

resented as a directed graph, or tree, and to calculate

the CO

e it is necessary to know the CO

e of each

preceding node that leads to a given node. After pro-

duction, it is necessary to also account for the car-

bon footprint that will still be added to it in its supply

chain (transport, storage, etc.).

The proposed platform allows the consumer to

trace the production chain of a particular product, ver-

ify the product’s origin, and verify how its carbon

footprint increments at each node of its value chain.

The next subsection presents the domain model

for the Smart Contract created to trace the carbon

footprint. A Smart Contract is ”a digital contract

that controls user’s digital assets, formulating the

participant’s rights and obligations” (Lin and Liao,

2017). Smart contracts are programs executed in the

blockchain to manage, secure and transfer digital as-

sets (Bragagnolo et al., 2018). Smart contracts de-

ﬁne a data structure and the operations used to interact

with these data, much like classes in object-oriented

paradigm (Watanabe et al., 2016).

3.1 Smart Contract’s Domain Model

A Product carbon footprint is the CO

e value of

producing a given output product from several in-

put products through a given Monthly Activity or se-

quence of monthly activities (see Figure 1) .

Figure 1: An output product’s monthly activity.

The domain model for tracing the environmental im-

pact, in the form of CO

e value emissions, of products

and organizations is depicted in Figure 2. The reading

of the domain model goes like this. An Organization

has multiple users and produces multiple products. A

product from an organization has carbon footprints,

which are calculated monthly based on the activities

that produced it. A monthly activity uses raw ma-

terials and other products in different quantities and

produces a certain quantity of one (ﬁnal or interme-

diate) output product. Intermediate products are not

targeted for the ﬁnal consumer, as is. Instead, they

will serve as input to a monthly activity in the same

or other organization, which will produce another ﬁ-

nal or intermediate output product.

Carbon Footprints of a given product refer to a

given product’s footprints over a period of different

months. Note that a product per se does not have an

associated CO

e value, the value used to account for

the environmental impact of the product. This value

is calculated monthly on the entity ProductFootprint.

This way, a product can improve or worsen its carbon

footprint from one month to the next. In reality, the

e values associated to a product (its ProductFoot-

print associated entity instances) are as many as the

monthly activities registered to produce that product

each month. This allows for a company to actively

Blockchain-based Traceability of Carbon Footprint: A Solidity Smart Contract for Ethereum

261

Figure 2: Contract domain Model.

seek to improve its products’ carbon footprints, and

thus its own company-wide carbon footprint, by opti-

mizing processes for trying to reduce the carbon foot-

print associated to its monthly ﬁxed costs (e.g. energy,

heating, water) or the carbon footprint of the monthly

activities to produce the chain of intermediate prod-

ucts that leads to the production of an end product.

MonthlyActivity (Figure 1) and MonthlyFixCost

are, then, the entities that register CO

e values relat-

ing, respectively, to the monthly activities that allow

producing a product, each month, and to the com-

pany’s ﬁxed costs, not directly related to a product’s

production process, but that are company-wide en-

vironmental costs indirectly associated to the com-

pany’s production activities, and thus must be divided

by all its produced products.

4 SMART CONTRACT

IMPLEMENTATION

4.1 Solidity Smart Contract

Solidity is a high-level programming language

used for implementing smart contracts on several

blockchain platforms, including in Ethereum (Bra-

gagnolo et al., 2018). It is an object-oriented

programming language whose syntax is similar to

JavaScript.

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262

Solidity has the possibility of creating data struc-

tures that go beyond basic data types, including the

possibility of value mappings and the inheritance be-

tween contracts. A contract’s state variables are per-

manently stored in contract storage, hence in the

Ethereum blockchain.

Solidity contracts will, after their publication, run

on the Ethereum Virtual Machine (EVM) and can be

invoked via their blockchain addresses.

Solidity implementation of the domain model pre-

sented before, needs that each entity is deﬁned as a

structure (struct). The main structures are listed next:

pragma solidity >=0.4.2;

contract CarbonFootPrint {

//-- Structures - Entities Implementation --

struct Product{

uint32 id;

string name;

string description;

bool intermediate;

uint32 idOrganization; //ref to Org.

uint32 idUnit; //reference to Unit

uint32[] productFootPrints;

//refs to ProductFootprint

}

struct ProductFootprint{

uint32 id;

uint32 co2eq; // base

uint16 exp; // exponent

uint32 idProduct;

uint32 year;

string month;

uint32 idMA; //ref to MonthlyActivity

}

struct MonthlyActivity{

uint32 id;

string description;

uint32 co2e;

uint16 exp;

string month;

uint32[] productQuantities;

//refs to input prod quantities

uint32 output; //ref to output Prod FootPrint

uint32 finalProductQty;

uint32 idOrganization;

uint32 idUnit;

uint32 idYear;

address idUser;

unit32[] productionCosts;

}

struct MonthlyFixedCost{

uint32 id;

uint32 co2e;

uint16 exp;

string description;

uint32 quantity;

string month;

uint32 idCostType;

uint32 idOrganization;

uint32 idYear;

}

Unsigned integers (uint16, uint32) have been used

for every numeric type, because Solidity currently

does not support signed integers (int). It also does

not support ﬂoating point numbers, such as f loat

or double. This way, every decimal value is imple-

mented through a base integer value and an exponent.

See, for instance, the CO2e attribute in the Product

Footprint Entity, which contains a product’s carbon

footprint CO

e value, and is implemented through

uint32 co2eq; uint16 exp; in the corresponding

contract struct.

The contract’s state variables are deﬁned through

mappings, which allow the recording of data collec-

tions in the blockchain.

mapping(uint32 => Product) public products;

uint32 public productsCount;

mapping(uint32 => MonthlyActivity)

public mactivities;

uint32 public mactivitiesCount;

mapping(uint32 => Organization)

public organizations;

uint32 public organizationsCount;

mapping(uint32 => MonthlyFixCost)

public mfixcosts;

uint32 public mfixcostsCount;

mapping(uint32 => Unit) public units;

uint32 public unitsCount;

mapping(uint32 => ProductCost)

public productCosts;

uint32 public productCostsCount;

mapping(uint32 => CostType)

public costsTypes;

uint32 public costsTypesCount;

mapping(uint32 => ProductFootprint)

public productFootPrints;

uint32 public pfootPrintCount;

mapping(uint32 => ProductQuantity)

public productsQuantities;

uint32 public productsQuantitiesCount;

An Event may be deﬁned in the smart contract for be-

ing emitted, or ﬁred, by some function. Fired events

are stored in logs by Ethereum and may be captured

by the distributed application code interfacing with

the smart contract for triggering some action at the

user interface level.

Blockchain-based Traceability of Carbon Footprint: A Solidity Smart Contract for Ethereum

263

event registUserEvent (

address indexed _candidateAddress

);

When the contract is issued, it is created through

a constructor, much like objects and classes.

We deﬁned the following constructor for the

CarbonFootPrint contract, so that the contract cre-

ating user is registered as the ﬁrst user (admin), and

a set of units is created on the units mapping (corre-

sponding to the entity Unit), and year 2019 is stored

as the ﬁrst year for monthly activities and ﬁxed costs

registration:

//- CONSTRUCTOR AND DEFAULT VALUES SETTING

constructor () public{

users[msg.sender] = User(msg.sender, 0, true);

arrayUsers.push(msg.sender);

// -- Initalize units

addUnit("tonne", "t", 10, 0, 1, false);

addUnit("kilogram", "kg", 10, 3, 1, true);

addUnit("gram", "g", 10, 6, 1, true);

addUnit("milligram", "mg", 10, 9, 1, true);

}

A particularity of this type of contracts is that their

deployment always has costs associated with being

implemented in Ethereum. Whenever a query oper-

ation is performed, a certain amount of gas/ether is

deducted from the requesting user’s account. There

are, however, some mechanisms that must be imple-

mented so that, if an error occurs, that user is not dis-

counted the full amount for something that may not

be effective in the blockchain.

The contract has functions for managing allowed

users, such as verifying if a user is registered for using

the contract and creating a new user (addUser):

function addUser (address _userResp,

address _user, uint16 _tipo,

uint32 _organization) public {

require(

users[_user].user_add == address(0),

"User already registered"

);

if(_tipo == 0 || _tipo == 1){

require(users[_userResp].tipo == 0,

"You need admin permissions");

}else if(_tipo == 2){

require(users[_userResp].tipo == 1 ,

"You need organization admin

permissions");

}

users[_user] = User(_user, _tipo, true);

arrayUsers.push(_user);

userOrganizations[_user].

push(_organization);

emit registUserEvent(_user);

}

Function require() serves for validation and, when

failing, returns an opcode and effectively reverses the

transaction and returns to the user the gas (the cost of

the operation) that has not yet been spent

Other functions for managing users include block-

ing and unblocking a user account.

The contract also allows for registering or-

ganizations, of which carbon footprints must be

traced/monitored. And, of course, the contract has

functions for registering new products:

// -- Add New Product Function --

function addProduct(string memory _name,

string memory _description,

bool _intermediate,

uint32 _org,

uint32 _unit,

uint32[] memory _footPrints) public

{

bool exist = false;

require(users[msg.sender].idOrganization == _org,

"You need to belong to the organization");

require(organizations[_org].id != uint32(0),

"Organization doesn’t exist");

for(uint32 i=1; i <= productsCount; i++){

string memory name = products[i].name;

if(keccak256(abi.encodePacked(name)) ==

keccak256(abi.encodePacked(_name))){

exist = true;

}

require(!exist, "Product already registered");

productsCount++;

products[productsCount] =

Product(productsCount, _name,

_description, units[_unit].initials,

_intermediate, _org, _unit, _footPrints);

organizations[_org].products.push(productsCount);

}

Another important function is the one that allow to

create information for a product’s carbon footprint, an

organization’s monthly ﬁxed cost, and a new monthly

activity for producing a given output product:

// -- Add New Product Footprint Function --

function addFootPrintProd(uint32 _co2eq,

uint16 _exp, uint32 _idProd,

uint32 _year, string memory _month,

uint32 _idMa) public {

require(users[msg.sender].idOrganization

== products[_idProd].idOrganization,

"The product doesnt belong

https://solidity.readthedocs.io/en/v0.6.0/

ICEIS 2020 - 22nd International Conference on Enterprise Information Systems

264

to your organization");

require(products[_idProd].id != uint32(0),

"Product doesn’t exist");

pfootPrintCount++;

productFootPrints[pfootPrintCount] =

ProductFootprint(pfootPrintCount, _co2eq,

_exp, _idProd, _year, _month, _idMa);

products[_idProd].productFootPrints.push(

pfootPrintCount);

}

The full contract and the whole

project sources can be found at:

https://github.com/xicosantos98/CarbonFootPrint.

4.2 Smart Contract Validation

For validating the contract, at development phase, a

set of test cases have been deﬁned. Before each test

case, a test contract instance is deployed on a meta-

mask test Ethereum blockchain:

beforeEach(’setup contract for each test’,

async function () {

cfootprintInstance = await

CarbonFootPrint.new();

users_count = await

cfootprintInstance.getUsersCount();

})

This section presents some example test cases.

Among other test cases, we need, for instance, to as-

sure that the contract allows to create a new organiza-

tion:

it("allows to create new organization",

async function() {

var name = "Lidia e Costa";

await cfootprintInstance.addOrganization(

name, [], [], []);

var organization =

await cfootprintInstance.organizations(1);

assert.equal(name,

organization.name);

})

It is possible to create a new product:

it("allows to create new product",

async function(){

await cfootprintInstance.addProduct(

"Fabric",

"10 kg of fabric",

true, 0, 2, []);

assert.equal(1, await

cfootprintInstance.productsCount());

})

It is possible to create a new product carbon footprint:

it("allows to create new product footprint",

async function(){

await cfootprintInstance.addProduct(

"Fabric",

"10 kg of fabric",

true, 0, 2, []);

await cfootprintInstance.addFootPrintProd(

324, 3, 1, 0);

assert.equal(1, await

cfootprintInstance.pfootPrintCount());

})

And, it is possible to create a new product’s monthly

activity:

it("allows to create new monthly activity",

async function(){

await cfootprintInstance.addMonthlyActivity(

"packing", 353, 5000, 3,

"April", [], 0, 0, 2, 1);

assert.equal(1, await

cfootprintInstance.mactivitiesCount());

})

Figure 3: Platform Architecture.

5 DISTRIBUTED APPLICATION

The distributed application (DApp) platform has been

implemented in a distributed layered architecture

comprised by the layers shown in Figure 3:

• A bottom distributed and decentralized persis-

tence layer, comprised by the developed smart

contract on top of the Ethereum Blockchain (the

Trufﬂe suite

has been used during development,

for supplying a local Ethereum development envi-

ronment and testing framework).

• A NodeJS middleware, which accesses the smart

contract through Web3.js libraries

and provides

www.trufﬂesuite.com

web3js.readthedocs.io/en/v1.2.1/

Blockchain-based Traceability of Carbon Footprint: A Solidity Smart Contract for Ethereum

265

Figure 4: DApp screen for creating a monthly activity.

Figure 5: Screen showing the traceability tree for a product’s carbon footprint in a given month.

an API that allows to interact with the smart con-

tract on a local or remote Ethereum node.

• A React-based distributed application that runs

on Ethereum enabled browsers (e.g.: a browser

with a plugin for Ethereum DApps, such as Meta-

mask

The carbon footprint DApp is based on an Ethereum

browser extension for letting an Ethereum user to cre-

ate and manage their own identities (via private keys,

local client wallet and hardware wallets). We used

Metamask for this purpose. This way, Carbon Foot-

print DApp users must authenticate themselves with

an Ethereum account, before being able to access the

DApp. This ensures a secure interface to access the

carbon footprint smart contract on Ethereum.

metamask.io

The DApp allows an organization, which wants

to monitor its products’ and monthly activities’ car-

bon footprints, to register itself on the platform. A

platform admin user must conﬁrm each organization’s

registration. Then, the organization admin may create

other organization’s user accounts. Each user account

is indeed the registration of an Ethereum user on the

platform, being given to it a speciﬁc user proﬁle on

the carbon footprint DApp.

An organization may create products on the plat-

form and, for a given product (output product),

monthly activities may be created (Figure 4), which

may “consume” input products. A product’s car-

bon footprint is calculated based on the carbon foot-

print of the monthly activity that creates it in a given

month, the carbon footprints of the input products of

the monthly activity, and the indirect organizational

ICEIS 2020 - 22nd International Conference on Enterprise Information Systems

266

monthly ﬁxed carbon footprints’ in the same month.

Any DApp user may access a dashboard with a se-

lection of products’ carbon footprint values and, for

each product, a traceability graph/tree may be con-

sulted (Figure 5).

6 CONCLUSIONS AND FUTURE

WORK

This paper presented the conceptualization, develop-

ment and validation of a distributed platform applica-

tion based on the Ethereum blockchain. The platform

allows a consumer to follow the chain of production

of a product, verify its origin, and have access to the

quantiﬁcation of the carbon footprint that the prod-

uct has caused in the environment. This way when

consumers need to decide which product to buy (or

consume) they can decide more consciously, based

on valid information (and can choose the most en-

vironmentally friendly product). The organizations

that produce the traced products also beneﬁt from

this platform by improving their reputation for ac-

tively improving their effectiveness at the environ-

mental level and for contributing to the well-being

of the planet. This will improve their image to con-

sumers and consequently improve their sales.

Some difﬁculties have been overcome, related to

the Solidity data structure limitations, namely the so-

lidity version being used does not support signed inte-

gers nor ﬂoating point numbers, among other issues.

Future work will address developing a tool for per-

forming data analyzes on the data stored in the smart

contract. We hope to be able to answer questions re-

lated to which products and types of products have the

highest carbon footprint and, within products of the

same type, which have the lowest carbon footprint,

and whether the footprint is increasing or decreasing

over time, etc.

Other future work is related to modifying the

smart contract so that, rather than making one ex-

tremely long contract, its code could be split across

multiple contracts. Solidity offers inheritance to make

this possible. Other way of reducing the contract, and

the associated transaction costs, is by putting in the

contract only the traceability data, moving users, or-

ganizations and other data to a database in the cloud.

ACKNOWLEDGEMENTS

The software resulting from this research work has

been developed as a curricular project by the second

and third authors, and has been partially funded by

project ValorMar - Valorizac¸

ao Integral dos Recursos

Marinhos - POCI-01-0247-FEDER-024517.

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